First, let me query you on why you might imagine that pulling back your foreskin could, or in what way it could impede you from "having sex"?
Just as a hint, I
actually visualise masturbation as a form of "having sex", albeit limited, and I'll take a punt that you have been masturbating, for some time, with no problems at all. So, how would any other form of "sex" differ?
I usually point out, as it gets a bit tedious to repeat it all, that your answer is in the previous postings on this discussion board, if you read back through sufficiently many. And indeed, that is a very
good idea in itself as not only will you learn about stretching, but some important things about the function of your penis, and what sexual relations are all about, into the bargain.
I note however, that the "nitty gritty" matters of stretching do tend to get overlaid by all the various questions, so will attempt to summarise it.
While you hold the foreskin open as Jim will no doubt illustrate, you have to get another finger, your little
finger tip to start, into
the "funnel" you see. You may need that finger to have a spot of lubrication (perhaps saliva will do) on it but of course, you do not want the other fingers holding the opening to be slippery. The important thing is that you have your foreskin stretched forward
so that there are no wrinkles on the inside to block your finger; if the finger is well manicured (smooth, short nail), it should eventually slip into the tight section and even through so that it is quite inside the foreskin and can feel the glans directly (which will not be uncomfortable if the finger is actually lubricated).
Once you get one
little finger in, you then progress (in due course) by practicing getting bigger fingers in until you get to your thumb and once you can do that, two little fingers. Then
you will be able to do what the "suddenlink" diagram
illustrates, levering your fingers apart
to achieve the full degree of stretch to an easily retractable foreskin.
Getting something into the narrow part may appear difficult, but is dead easy if you look at it the right way round! What you do is to hold the end of your foreskin - preferably the underside as illustrated so frequently in the instructions to stretch your frænulum, and put it on the stretch pulling away
from your body.
This stretches out any folds or pleats in the skin on the inside (and indeed, on the outside) of your foreskin and means the narrow part is now on the inside
of effectively, a funnel. By pulling the foreskin forward against whatever - whether a pen cap, a finger, or a crafted stretching device - that object will simply slide inside through the foreskin. Some lubricant on the device - and the device only, not the fingers you are using to grip the foreskin - will make it easier and avoid unpleasant sensations when it touches the glans, which it however is less likely to do as you are stretching the foreskin away
from the glans anyway.