Use this card's effect to send "Treeborn Frog" to the graveyard. Then next turn after "Treeborn Frog" is Special Summoned, use the effect of "Swap Frog" to return "Treeborn" and get a second Normal Summon.
You can also send "Ronintoadin" to the graveyard and use its effect later in the game.
Discard "Ronintoadin" to summon this card, then send a Frog to the grave with its effect, or vice-versa. Then, banish the Frog to Special Summon "Ronintoadin" and get 2 monsters on your side of the field without using your Normal Summon for the turn.
You can always re-use the effect of "Swap Frog" to summon himself and bounce himself back as long as you can pay his cost to discard a WATER-Attribute monster.
When combining this card with "Ultimate Offering", "By Order of the Emperor" and "Solemn Wishes" you can draw infinite cards by summoning it, negating it's effect and drawing a card, gain Life Points, returning it to the hand and then pay the cost to summon it again, negating it's effect and so on.
Use the "Salvage" combo above to send a "Substitoad" from you deck to the graveyard. Then, use "Salvage" to add "Substitoad" and the monster used to Special Summon "Swap Frog" to you hand. Then you can summon "Substitoad" and use it's effect to tribute for any frog from your deck. (Most likely a defense position "Dupe Frog")
You can use this same combo to summon 3 "Des Frogs". First use the above combo to summon a "Substitoad" and "Swap Frog". Then use the effect of "Substitoad" to summon another "Swap Frog" by tributing the first "Swap Frog" and using its effect, send a "T.A.D.P.O.L.E." to the Graveyard. The do the same again by summoning another "Swap Frog". Then use the effect of "Substitoad" to tribute itself and summon a "Des Frog" from your deck. Then use "Swap Frog's" effect to return "Des Frog" to your hand. Then Tribute "Swap Frog" to tribute summon "Des Frog" for "Swap Frog's" effect. Then, since there are 2 "T.A.D.P.O.L.E.s" in the graveyard, you can summon 2 more "Des Frogs" from your deck.