If your toilet is leaking at the base or bottom when flushing it then that means that your wax ring has gone bad and needs replaced.
It's easy to do as you just unbolt the old toilet and set it aside after unhooking the water lines and then you set the toilet on it's side and clean off the old wax from the toilet bowl and the toilet drain flange.
Then put the wax ring on the toilet flange and then position the toilet back over it using the bolts as a guide.
Press firmly on the toilet and then snug down the bolts one side at a time. Don't tighten the bolts too much though since you can crack the toilet bowl.