You can install applications different ways. Terminal, the Ubuntu Software Center, and Synaptic.

With the Ubuntu Software Center, you just open it from the Launcher, and search for the application that you want.

If you know the right commands to install via terminal, then you'd just press Ctrl+Alt+T on your keyboard to open Terminal. When it opens, you can run the command(s) needed to install the application.

For synaptic, it has to be installed on you system. To install it, just press Ctrl+Alt+T on your keyboard to open Terminal. When it opens, run the command(s) below:

sudo apt install synaptic

Once installed, you can open it, and search for the application that you want to install, and just mark it for installation.

Also in some cases, you have to download either a .deb file in case of your question about Chrome, and have to manually install it, or a .tar.gz file, and that also have to done manually.

Now as far as Chrome is concerned, you can install it by downloading the .deb file, or just press Ctrl+Alt+T on your keyboard to open Terminal. When it opens, run the command(s) below:

For 32bit

wget https://dl.google.com/linux/direct/google-chrome-stable_current_i386.deb
sudo dpkg -i google-chrome-stable_current_i386.deb

For 64bit

wget https://dl.google.com/linux/direct/google-chrome-stable_current_amd64.deb
sudo dpkg -i google-chrome-stable_current_amd64.deb

If you encounter any error during the installation, when its done do

sudo apt -f install

For pros and cons of the different ways to install see this Post.

_{^{Source for Chrome installation: Google}}

Addition

Installing software in Ubuntu can be done several ways:

Ubuntu Software Center

You can search for an application, or go through the categories:

Synaptic Package Manager

You can search for an application, or go through the categories:

Installing via Terminal

Installing from terminal can be done in several ways:

APT
You can search for an application. The command to search for software is:

apt search <application_name>

Adding Repositories:

Edit the sources list file, and add

sudo -H gedit /etc/apt/sources.list

Or add from terminal

sudo add-apt-repository <repository_name>
sudo apt update
sudo apt install <application_name>

Others ways you can install

Manual download of a .deb (Debian package):

• Once downloaded, you can double-click on the package to have it open in the Software Center, from where you can install it.

• Or, just press Ctrl+Alt+T on your keyboard to open Terminal. When it opens, navigate to the download location, and run the command(s) below:

  sudo dpkg -i <package_name>.deb
  

Other options:

• .rpm files are packaged for Fedora or Mandriva, but you can use alien (you can install using Synaptic) that allows you to convert .rpm files to .deb. (may not work all the time)

• .tar.gz files are compressed. If you see the .tar.gz, it could be compressed files that have a pre-compiled binary file, or files that have the source code allowing you to compile the application from source. To find out how to install from a .tar.gz, see How to install from a .tar.gz.

For more info see Installing Software, or A beginners guide to installing programs in Ubuntu

In Ubuntu 16.10 and later indicator-multiload is in the universe repository. Search the Software application for System load indicator. Alternatively you can also find the System load indicator by searching for the package's name (indicator-multiload). If System load indicator doesn't appear in the Ubuntu 16.10 Software app, this is a bug like this one: Missing package names in Ubuntu Software Center. It should be reported it as a new bug, since that bug was reported 4½ years ago and it happened when using a different application.

You an also download the .deb files for indicator-multiload for Ubuntu 16.10 manually.

• Download Page for indicator-multiload_0.4-0ubuntu4_amd64.deb on AMD64 machines
• Download Page for indicator-multiload_0.4-0ubuntu4_i386.deb on Intel x86 machines