Cowboy/cowgirl or reverse cowboy/cowgirl sex position
In these positions the receptive partner is on top of and straddling the penetrative partner either facing the penetrative partner or facing away ("reverse") from the penetrative partner.
This is a great beginning position, as this position allows the receptive partner more control over the depth, rhythm and speed of penetration. More specifically, the receptive partner can slowly push his/her anus down on the penis, allowing time for the anus muscles to relax around the penis before the receiving partner decides to start riding up and down on the penis.