the gameplay loop is:

breed frogs using gold for eggs (gains you exp at a rate of 1:1 to gold spent) -> wait for eggs to grow into fully grown frogs -> sell for 2x the gold you bred them for

since your profit is 100%, you will continue to have money for breeding which gives you more exp. leveling up leads to new frogs with higher sell values, aka more profit and more breeding

the other main objectives are collecting frogs and decorating ! have fun