i dont think loosing weight should be your first goal, go find out ur bfat% or post a pic of urself.
you will find, if you start lifting weights you will loose some fat and tone up alot.
also, if u try and loose weight first, you will find it harder to gain just muscle later, alot of people try this and end up putting the fat back on (body not used to all the extra calories, and uses them as fat)
basically, if u have a caloric deficite, your body will try and get every last calorie out of your food, so when you stop loosing weight and try to bulk up, your body will still be trying to add fat.
the benefits of lifitng first are the following:
because you havent done much, you will still loose fat, when i started i gained weight, gained muscle, and lost over 2" off my waist.. and this was with no cardio at all.
the second benefit is that when you then start to get serious about loosing your excess fat, your body will have more muscle, so the amount of calories you burn each day will have gone up, and through this you will loose fat faster (also you will be working on increasing your metabolic rate, so will maintain alot more muscle)
basically theres 2 ways of doing it:
gain muscle, then loose fat.
loose fat, then gain muscle.
6ft and 100kgs, i think you should gain muscle first then loose the fat.
when i started i gained muscle then loost fat, im 5"11 and was 105kg when i started. that was 6months ago and im starting my cutting now, and its going really well.
I reckon you should go speak to sum1, go to a vitamen store go find the biggest guy you can, and tell him where you are and what your goals are.
If you really just want to be skinny, then just go run. if you REALLY want to be strong, get the muscles then loose the excess.
if you do decide to get lifting, eat alot more and buy some protein, (horleys ice i reccomend) aim for 2500-3500 cals a day.
if you decide to start running, work on a calorie deficit, eat less, run more to make it simple.
just know, if you lift, you will loose some fat aswell. if you run, you will loose muscle aswell.
now that your informed, make your decision and then we can figure out what to do next
ps. go to your gym and ask for a bfat% measure. I think you will be suprised.
pss. post a pic of who u want to look like, that helps aswell.