Most commonly used change command takes the following form.
Replace the content of the region determined by the motion command motion-command by the text you type. If the motion command is a point command then you will type the text into minibuffer, and if the motion command is a line command then the region will be deleted first and you can insert the text in insert mode.
For example, if point is at the beginning of a word ‘foo’ and you wish to change it to ‘bar’, you can type c w. Then, as w is a point command, you will get the prompt ‘foo =>’ in the minibuffer, for which you can type b a r RET to complete the change command.
Change a line. Given a count, that many lines are changed.
Change current region.
Expand current region and change it.