Bet Slip: The Bet Slip is the 'cart' of a Sportsbook. It's an area containing selected picks and where you enter your wager amount(s) before confirming your bet(s). Bet Receipt: A bet receipt is the confirmed 'ticket' of a placed bet.
If you want to place a bet, you must first add a selection to your bet slip. In order to do this, you simply need to click on the 'Odds' (i.e. 3/1) next to the selection you've bet on. This will add the selection to your betslip.