Emacs keys are often confusing to beginners. Here's a summery.
• 【Alt+x】 is to call a command by name.
• 【Ctrl+‹letter›】 is for frequently used editing commands. ⁖ cursor movement, Paste C-y, mark C-SPC, Cancel C-g, Search C-s, ….
• 【Alt+‹letter›】 is for somewhat less frequently used operations, often complement to Ctrl. ⁖ move by words {M-f, M-b}, Copy M-w, comment-dwim M-;, ….
• 【Ctrl+x …】 is for commands that are useful globally. ⁖ dired C-x d, switch-to-buffer C-x b, string-rectangle C-x r t, bookmark-bmenu-list C-x r l, ….
• 【Ctrl+c …】 is for major-mode specific commands. ⁖ in org-mode, org-time-stamp C-c . inserts date.
• 【Ctrl+h …】 or 【F1 …】 is for help or getting info. ⁖ describe-function C-h f, apropos-command C-h a, info C-h i.
• 【Ctrl+Alt+‹key›】 is for lisp coding related commands. ⁖ backward-sexp <C-M-left>.
(Tutorial: How to Edit Lisp Code with Emacs.)
Note 【Alt+x】 is technically 【Meta+x】, ususually written as M-x. “Meta” is a physical key on lisp machine keyboards. If you are on a text terminal, and no Meta remapping has been setup, you can type 【Meta+x】 by pressing 【Esc x】.
〔☛ Space-cadet Keyboard and Lisp Machine Keyboards〕
See also: A Curious Look at GNU Emacs's 1000+ Default Keybinding.