Installing cocoapods to macOS Catalina

In my mac mini I've running Catalina 10.15.7. I've also installed Xcode 12.4. Now as I'm using third party library I'm trying to install cocoapods in my mac.
So I used this –

sudo gem install cocoapods

which I got from official website.

But I'm getting this –

Password:
Fetching concurrent-ruby-1.1.8.gem
Fetching fuzzy_match-2.0.4.gem
Fetching i18n-1.8.10.gem
Fetching thread_safe-0.3.6.gem
Fetching tzinfo-1.2.9.gem
Fetching activesupport-5.2.5.gem
Fetching nap-1.1.0.gem
Fetching httpclient-2.8.3.gem
Fetching algoliasearch-1.27.5.gem
Fetching ffi-1.15.0.gem
Fetching ethon-0.12.0.gem
Fetching typhoeus-1.4.0.gem
Fetching netrc-0.11.0.gem
Fetching public_suffix-4.0.6.gem
Fetching addressable-2.7.0.gem
Fetching cocoapods-core-1.10.1.gem
Fetching claide-1.0.3.gem
Fetching cocoapods-deintegrate-1.0.4.gem
Fetching cocoapods-downloader-1.4.0.gem
Fetching cocoapods-plugins-1.0.0.gem
Fetching cocoapods-search-1.0.0.gem
Fetching cocoapods-trunk-1.5.0.gem
Fetching cocoapods-try-1.2.0.gem
Fetching molinillo-0.6.6.gem
Fetching atomos-0.1.3.gem
Fetching colored2-3.1.2.gem
Fetching nanaimo-0.3.0.gem
Fetching xcodeproj-1.19.0.gem
Fetching escape-0.0.4.gem
Fetching fourflusher-2.3.1.gem
Fetching gh_inspector-1.1.3.gem
Fetching ruby-macho-1.4.0.gem
Fetching cocoapods-1.10.1.gem
Successfully installed concurrent-ruby-1.1.8
Successfully installed i18n-1.8.10
Successfully installed thread_safe-0.3.6
Successfully installed tzinfo-1.2.9
Successfully installed activesupport-5.2.5
Successfully installed nap-1.1.0
Successfully installed fuzzy_match-2.0.4
Successfully installed httpclient-2.8.3
A new major version is available for Algolia! Please now use the https://rubygems.org/gems/algolia gem to get the latest features.
Successfully installed algoliasearch-1.27.5
Building native extensions. This could take a while...
ERROR:  Error installing cocoapods: 
        ERROR: Failed to build gem native extension.

current directory: /Library/Ruby/Gems/2.6.0/gems/ffi-1.15.0/ext/ffi_c/System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/bin/ruby -I/System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/lib/ruby/2.6.0 -r ./siteconf20210406-1384-1vtmk4p.rb extconf.rb
checking for ffi.h... *** extconf.rb failed ***
Could not create Makefile due to some reason, probably lack of necessary libraries and/or headers.  Check the mkmf.log file for more details.  You may need configuration options.

Provided configuration options:
    --with-opt-dir
    --without-opt-dir
    --with-opt-include
    --without-opt-include=${opt-dir}/include
    --with-opt-lib
    --without-opt-lib=${opt-dir}/lib
    --with-make-prog
    --without-make-prog
    --srcdir=.
    --curdir
    --ruby=/System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/bin/$(RUBY_BASE_NAME)
    --with-ffi_c-dir
    --without-ffi_c-dir
    --with-ffi_c-include
    --without-ffi_c-include=${ffi_c-dir}/include
    --with-ffi_c-lib
    --without-ffi_c-lib=${ffi_c-dir}/lib
    --enable-system-libffi
    --disable-system-libffi
    --with-libffi-config
    --without-libffi-config
    --with-pkg-config
    --without-pkg-config
/System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/lib/ruby/2.6.0/mkmf.rb:467:in `try_do': The compiler failed to generate an executable file. (RuntimeError)
You have to install development tools first.
    from /System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/lib/ruby/2.6.0/mkmf.rb:585:in `block in try_compile'
    from /System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/lib/ruby/2.6.0/mkmf.rb:534:in `with_werror'
    from /System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/lib/ruby/2.6.0/mkmf.rb:585:in `try_compile'
    from /System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/lib/ruby/2.6.0/mkmf.rb:1109:in `block in have_header'
    from /System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/lib/ruby/2.6.0/mkmf.rb:959:in `block in checking_for'
    from /System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/lib/ruby/2.6.0/mkmf.rb:361:in `block (2 levels) in postpone'
    from /System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/lib/ruby/2.6.0/mkmf.rb:331:in `open'
    from /System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/lib/ruby/2.6.0/mkmf.rb:361:in `block in postpone'
    from /System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/lib/ruby/2.6.0/mkmf.rb:331:in `open'
    from 
/System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/lib/ruby/2.6.0/mkmf.rb:357:in `postpone'
    from /System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/lib/ruby/2.6.0/mkmf.rb:958:in `checking_for'
    from /System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/lib/ruby/2.6.0/mkmf.rb:1108:in `have_header'
from extconf.rb:10:in `system_libffi_usable?'
from extconf.rb:42:in `<main>'

To see why this extension failed to compile, please check the mkmf.log which can be found here:

/Library/Ruby/Gems/2.6.0/extensions/universal-darwin-19/2.6.0/ffi-1.15.0/mkmf.log

extconf failed, exit code 1

Gem files will remain installed in /Library/Ruby/Gems/2.6.0/gems/ffi-1.15.0 for inspection.
Results logged to /Library/Ruby/Gems/2.6.0/extensions/universal-darwin-19/2.6.0/ffi-1.15.0/gem_make.out

I've seen this question but my ruby version is –

ruby 2.6.3p62 (2019-04-16 revision 67580) [universal.x86_64-darwin19]

I've also take a look in this but could not able to solve the problem.

Edit:
I've used this –

xcode-select --install

but got –
xcode-select: error: command line tools are already installed, use "Software Update" to install updates

So, Is there any ruby dependency I've to install first or I just missed something?