for any exersice regiment I suggest you talk to a doctor as you are starting out. especially if you are over 35 years old, haven't worked out in a long time/never, or have had health problems in the past....
younger person and a noob- you need to ease yourself into the exersice schedule to avoid an injury that could set you back months. after your body gets used to the 'after workout burn' - start looking at supplements but don't just take them for the hell of it. you need to take them for a specific purpose and for good reason.
if not like somebody else said - all that will just be washed out of the body through expensive urine....
the rest is human phisiology and is not too complicated:
if you want to gain weight - you need to take in more calories than your body burns.
if you take in mostly 'sugar' calories - you will gain fat weight. if you take in more 'protein' calories you gain muscle, but only if you are working out to build muscle.
there's a thing about gaining more muscle - those muscles need to be put to work. muscle when it is not used turns to fat and gets stored. and burning off fat is very time consuming and difficult.....
a lot of people fail at their workout goals just because they don't understand calories and how taking in more calories(eating more) can translate to fast weight loss / muscle gain when paired with a good exercise program.
i believe that unless you are looking for a 'body builder' type body with extremely low water retention, very low body fat, a lot of 'cut' muscle, veins popping and lots of muscle you don't need to take supplements.
they help, especially recovering, but are not 'necessary' for us mere mortals who want to just be healthy or look a bit better in a swimsuit....... it all depends on your goals.