For a Standard Trifecta you have to select first, second and third in the correct finishing order. This gives you just one combination to win.
A Box Trifecta increases your chance to win a Trifecta. By 'boxing' your selections you cover all the possible combinations involving those runners. For example, three (3) runners boxed will cover all six (6) possible combinations. You can box as many runners as you like.
A Multiple Trifecta allows you take as many runners as you like for each placing. For example, you can take three (3) runners for first, five (5) runners for second and twelve (12) runners for third. Providing one of your runners selected for first runs first, one of your runners selected for second runs second and one of your runners selected for third runs third then you win the Trifecta.
If you feel there is a 'sure thing' to win a race, then a Banker Trifecta might be for you. You could make your 'sure thing' a Banker and couple it with two (2) or more runners to finish second and third. Your Banker has to win the race and your selections for second and third must finish second and third to win the Trifecta.
If you have a 'sure placegetter', you can take it as a Roving Banker Trifecta with two or more other runners. Providing your Roving Banker selection runs a place and your 'other' selections fill the other placings then you win the Trifecta. Likewise, if you have two (2) 'sure placegetters', you can take those two as a Double Roving Trifecta with one or more other runners. Providing your two (2) Double Roving selections run two of the placings and one of your other selections fills the remaining placing, you win the Trifecta.