What are some excellent Emacs utter beginner resources

I don't know what's causing this problem or how to fix this, but I can offer a workaround for most purposes.

Normally, dead keys are processed at a very low input layer, not even visible from Lisp. But you can do the processing in Lisp.

If you want the keys to act as dead keys:

There is already a limited mechanism for dead keys in Lisp, designed for 8-bit character sets on machines that don't have any way to input non-ASCII characters. If you type C-x 8 followed by an accent and a letter, the corresponding accented letter is inserted, thanks to the iso-transl library. We can copy this mechanism. Put this in your .emacs:

(define-key key-translation-map [dead-grave] (lookup-key key-translation-map "\C-x8`"))
(define-key key-translation-map [dead-acute] (lookup-key key-translation-map "\C-x8'"))
(define-key key-translation-map [dead-circumflex] (lookup-key key-translation-map "\C-x8^"))
(define-key key-translation-map [dead-diaeresis] (lookup-key key-translation-map "\C-x8\""))
(define-key key-translation-map [dead-tilde] (lookup-key key-translation-map "\C-x8~"))
(define-key isearch-mode-map [dead-grave] nil)
(define-key isearch-mode-map [dead-acute] nil)
(define-key isearch-mode-map [dead-circumflex] nil)
(define-key isearch-mode-map [dead-diaeresis] nil)
(define-key isearch-mode-map [dead-tilde] nil)

The map key-translation-map rewrites key sequences as they are entered, so this will make dead ` a equivalent to à for most purposes. Explicitly setting entries in isearch-mode-map to nil is necessary because otherwise pressing a dead key would exit isearch before the translation could kick in.

If you want the accent characters to be inserted immediately

(define-key key-translation-map [dead-grave] "`")
(define-key key-translation-map [dead-acute] "'")
(define-key key-translation-map [dead-circumflex] "^")
(define-key key-translation-map [dead-diaeresis] "\"")
(define-key key-translation-map [dead-tilde] "~")

Short answer

It provides number 0 to the next command.

Long answer

C-u in emacs called universal-argument. It's begin a numeric argument for the following command. Digits or minus sign following C-u make up the numeric argument. You can read more details about C-u by typing C-h k C-u or read online documentation here.

Understanding meaning of C-u, now you can know that, C-u 0 C-k and C-k are not the same. The first, C-k is called with an numeric argument, it's number zero. The second C-k is called alone. It leads to different behavior.

From Killing by Lines section of emacs manual:

The simplest kill command is C-k (kill-line). If used at the end of a line, it kills the line-ending newline character, merging the next line into the current one (thus, a blank line is entirely removed). Otherwise, C-k kills all the text from point up to the end of the line; if point was originally at the beginning of the line, this leaves the line blank.

...

When C-k is given a positive argument n, it kills n lines and the newlines that follow them (text on the current line before point is not killed). With a negative argument −n, it kills n lines preceding the current line, together with the text on the current line before point. C-k with an argument of zero kills the text before point on the current line.