shrooms are one of the least dangerous drugs around. they can be intense to the point of real fear and paranoia (like thinking you've gone insane and actually believing it) if you take too much but they won't do any permanent physical damage.
the worst thing that can happen from any hallucinogen is something called hallucinogen persisting perception disorder where you have visuals in every day life, it sucks i know someone who had it but for the most part it went away after a few months-year and it's usually caused by acid as lsd is more potent. as long as you start off light with the shrooms you will have the most fun you've ever had in your life.
picking shrooms is difficult unless you know what to look for or have someone experienced with you, however if you break the stem and it isn't blue inside DON'T EAT IT.