You need to
seriously come up with an answer for this before you proceed.
Presuming you are the same poster as that immediately before this, you are not quite "normal" insofar as you have a tight foreskin and short frænulum. As explained, you
need to stretch both and need to read
heavily back through here to find the
multiple explanations we have given of the process of stretching these two areas.
So: How far does the penis go into the vagina? As far as you can, with due comfort to both parties.
How much of the foreskin is forced back or retracted? What makes you think sex involves "forcing"
anything? I hope you are not in any respect whatsoever modelling your concept of sex, on what is depicted in pornography lest you come up with some
really foolish ideas (such as not using condoms!

But that is merely
one stupidity in porn).
Just what makes you think that it is
necessary for the foreskin to retract for sexual activities? Do you need to retract it to masturbate? Why would you imagine intercourse to be different?
Once you master these questions, you will understand whether it matters just
how far the foreskin will retract. The fact that you are asking indicates that you
do want to do some stretching,but there is most certainly no hurry to achieve any particular result.
Do the reading, and find out!