v - start visual mode, mark lines, then do a command (like y-yank)
    V - start linewise visual mode
    Ctrl + v - start visual block mode

    o - move to other end of marked area
    O - move to other corner of block

    aw - mark a word

    ab - a block with ()
    aB - a block with {}
    at - a block with <> tags

    ib - inner block with ()
    iB - inner block with {}
    it - inner block with <> tags

    Esc - exit visual mode