The selection is done in visual mode.
To cut (or copy) and paste using visual selection:
1. Position the cursor at the beginning of the text you want to cut/copy.
2. Press v to begin character-based visual selection (or upper case V to select whole lines, or Ctrl-v for a vertical block).
3. Move the cursor to the end of the text to be cut/copied. (While selecting text, you can perform searches and other advanced movement, a feature that sets vim apart from most other editors.)
4. Press d (as in “delete”) to cut, or y (as in “yank”, which I imagine meaning “yank so hard and fast that it leaves a copy behind”) to copy.
5. Move the cursor to the desired paste location.
6. Press p to paste after the cursor, or P to paste before it.
Bonus Tip: To replace the selected text with new text (to be entered by you), press c instead of d or y on step 4. This deletes the selection and leaves you in insert mode. Then, instead of (or prior to) steps 5-6, type your replacement text.