First decide on what type of transportation you want to use. There are trains -only the EuroStar will/can bring you to the continent, IN the UK there is a dense but fairly expensive train network that can bring you to about any of the usual 1st timer touristy places. And there are BUSes and planes-and the odd ferry between ports. each has its pro and con-I guess you are smart enough to know that.

2.THIS forum is aimed at people using railpasses-the full info about these is on the main page, and there is ample country-information. I am aware that the multitude of countries, companies and lines/timings can be an enormous challenge for USAers, not quite used to that, the best advice is to just try out a few dummy trips. OR go to a site like seat61, from GB, which describes in finest detail all overland trips out from LON to all EUR countries. or a general touristy forum like tripadvisor-which is usually against using passes.

IF you decide on buying a trainpass, then you also have to take a look into HOW to make the various REServations needed for some trains (by far not all-here in UK you can board about any daytime trains without that-just find a seat listed as available=non reserved)-again info in main site.

3.Do be aware that LON is a very expensive city, that if you really want to do from there what your state-visit a lot of countries (and come back all the time??) this is not the best of choices-then base yourself more centrally somewhere ´on the continent´

maybe i didn’t explain myself very well.  my friend and i are going to be staying in london, we’ve already booked the flights and accomodations.  what we want to do is for example stay in london for two weeks, then go to france for a weekend and then go back to london for a couple weeks and then go to italy or spain or somewhere else for a couple nights.  what i am wondering is if i have to book that as separate trips or if i can book it all as one.

You'll need to book any reservations separately.

As to recording the journeys on the pass itself: whether you have a mobile or a paper pass, you'll need to do this separately for each journey.