Mountain bikes will have 26 inch tires and hybrid bikes will have 700c wheels like on a road bike but wider. You need to figure out where you are going to ride. Mountain bikes are very inefficient on the road and harder bike paths and hybrids are great on the road and can be ridden on smooth gravel paths like rail trails.
You need to measure your actual inseam.
Mountain bike inseam X .59 = frame size
Hybrid bike inseam X .65 = frame size
You want a stand over clearance of 2-4 inches on a mountain bike and 1-2 on a hybrid.
Stay away from Walmart and other department store bikes. They are junk and wont fit you, visit the local bike shops to see what they have and take some test rides. You want service after the sale.
You need to measure your actual inseam.
Mountain bike inseam X .59 = frame size
Hybrid bike inseam X .65 = frame size
You want a stand over clearance of 2-4 inches on a mountain bike and 1-2 on a hybrid.
Stay away from Walmart and other department store bikes. They are junk and wont fit you, visit the local bike shops to see what they have and take some test rides. You want service after the sale.