Depending on the spell, it may have different effects. If you cast a love spell on someone, it may do a few things. Like maybe make them notice you, or pay attention to you more. It could also make that person have false feelings for you, or become attached to you.
There is also the option of casting a love spell into the universe. Which is where the spell is not placed on a specific person, it is placed on love. It basically sends those energies into the universe, bringing love to you, rather than bringing a person to you.
Most people would recommend doing the latter. Simply because casting on a person may bend their will. There are also chances of backfiring if the spell is not done properly.