Cheatsheet: Vim

Normal mode (the default you land in) treats keystrokes as commands/motions, not text -- pressing 'x' deletes a character rather than typing it. Insert mode (entered with i, a, o, etc.) types text like a normal editor until you press Esc to return to normal mode. Visual mode (v for character-wise, V for line-wise, Ctrl-v for block-wise) lets you select a range of text with motions, then apply a command (d, y, c) to the whole selection. There's also command-line mode, entered with : (or / and ? for search), for ex-commands like :wq or :%s/foo/bar/g.

A text object is a noun (what to act on) that follows a verb (the operator) and a scope: i for 'inner' (excludes surrounding delimiters/whitespace) or a for 'a' (includes them). diw deletes the inner word under the cursor without touching surrounding punctuation/spaces; ci" deletes everything inside the nearest double quotes and drops you into insert mode to retype it; da( deletes a parenthesized expression including the parens themselves. This composability (operator + i/a + object: w/s/p/"/'/(/{/[ etc.) is what makes Vim edits fast once memorized -- you rarely need to select text manually.

:%s/old/new/g replaces every occurrence of old with new on every line (% means the whole file; omit it to affect only the current line). Add c for confirm-each-match (:%s/old/new/gc), or i for case-insensitive. To replace only within a visual selection, select the range first (V then move, or Ctrl-v for a block), then type : -- Vim auto-fills the range as :'<,'>, so you just append s/old/new/g. Use < and > around a word (<foo>) to match whole words only, not substrings.

:q quits the current window/buffer but refuses if there are unsaved changes. :wq writes (saves) then quits. :x is like :wq but only writes if the buffer was actually modified (a no-op save is skipped). :q! discards unsaved changes and quits anyway -- the ! is Vim's general 'force, I know what I'm doing' suffix, also seen on things like :w! (force-write a read-only file you have permission to overwrite).

A buffer is an in-memory copy of a file's contents (:ls lists open buffers; you can have many more buffers open than visible windows). A window (:split / :vsplit) is a viewport onto a buffer -- splitting your screen doesn't open a new file, it just gives you a second view, often onto the same buffer or a different one via :e. A tab (:tabnew) is a full-screen collection of windows/layouts -- think of it as a separate workspace, not a single file the way browser tabs are. Most experienced Vim users lean on buffers + splits for editing a project, and reserve tabs for a small number of distinct high-level layouts.