[jinky]

I really do think you should get to know your camera / photography a lot more before even offering free wedding services to the happy couples. Even doing it for free you will find people will have expectations and at the end of the day there is a chance of ruining that big day if you are not ready for it. It`s OK doing fun shots / guest shots with kit lenses and the like but to shoot a full wedding including service etc you need to have excellent fast pro level lenses and a camera body that copes well with low light to stand a chance of getting acceptable results. Flashes are often banned during services and unless you know what your camera and lenses are capable of it can be a nightmare. Your post gives it away that you are new in the game. You cannot confuse macro lenses - some of which might be F2.8 and excellent primes with fast general lenses that you need for weddings. I`d say you need a 24/28- 70 2.8 lemns, a 70-200 2.8 lens and maybe a prime 50/85 mm 1.8 lens backed up by a flash for those occasions when you can use it with facility for off camera use with diffusers or bounce facilities. I`d also expect you`d need back up body / lenses/ flashes to cover accidents/ breakdown or you would be doing any couple having the biggest day of their lives a disservice.
If you do get someone so desperate to take a free photographer with limited experience make sure you get soemthing written down in contract / by email that is agreed that lays down your levels of expertise and a commitment to do your best whilst recognising it is a free service so you can not be sued for ruining the big day!
Don`t underestimate how hard the day can be. I`ve done a handful and enjoyed them but was amazed how tiring it all was and how there is no break. Mine turned out ok but assisting on my first, where the main photographer had no expectations from me but was giving me experience, I was mortified when my D80 struggled in the darkest venue I`ve been in to cope with lighting conditions and though pleased with what I had got I was in awe with what the other guy shot with a top range camera and better lenses more suited to the setting. He used my shots to supplement his but I could not have given a full spread of the day with what I had available to me at that time even as an experienced photographer as my camera could not shoot cleanly above 1200 ISO