Why is there snails in my fish t..

Brief：
OK we have had this tank for about 3 months Id estimate and ALl we have put in thre is Rocks we bought at walmart fish and a few boat things we got at.. 

OK we have had this tank for about 3 months Id estimate and ALl we have put in thre is Rocks we bought at walmart fish and a few boat things we got at wlamart t odecorate and then 2 little plants we bought at an actual fish store, But lately we have been seeing snails in the tank at first there was only 1 now we have sen about 6 I know they mate and reproduce every few weeks but how could we have snails and where did they come from? I havent put any in there and everything we bought was either in bags or from actual fish stores themselves? SO how did they get in there? COuld their eggs have been hidden in the plant or something and just now hatching and now they are just reproducing or something?? SHould I keep taking them out or let them stay in there??

You got your snails from unwashed gravel and/or real plants. They lay their eggs in a jelly-like form usually attached to rocks or stones or plants. They're hermaphrodite (both male and female) so they reproduce on their own really fast! They continue to live, eating left-over food, algae, and even fish wastes.

Should you take them out? It depends. They can be beneficial to your tank because they help control water and glass pollution by eating algae and left-over food. However, they tend to overpopulate and might take too much aquarium space. If that ever happens, they'd compete with your fish for oxygen in your water, as well as food. Snail population control must therefore be put in place.