what is better to do!?

Weightlifting, then cardio.
or
Cardio, then weightlifting.

Also,
When I work out, I do exercises for each group of muscles.

I heard that I shouldn't be doing that? Like I should take days and work only a few groups at a time like shoulders and arms and legs and back instead of an all around workout?

Confused.

Don't know there's a rule for that, find what works best for you. Personally, I like to have more energy for weight lifting and do weights first. I don't feel like i need tons of energy for the light cardio I do. Or even if I do sprint work I'm fine doing it second.

Weight lifting then cardio.

Basically, if you are lifting you aren't able to burn body fat unless you go really light and speed it up to make it cardio. Weight training burns muscle glycogen. One of the by-products of glycogen metabolism is pyruvate. Pyruvate is needed to be able to start the fat burning process. If you don't do cardio after weight training, then the pyruvate will be converted to lactic acid and you will have muscle pain for about 6 hours while they are trying to clear the lactic acid. Cardio can burn either glycogen or fat. If you don't have enough pyruvate for fat burning, then the body will burn glycogen to make it so not all of your cardio time is actually spent burning fat. If you do cardio after weight training, though, then there is plenty of pyruvate available for the chemical reaction that is fat burning so all of your cardio time can be spent in fat burning.

So, if you do weight training first, followed by cardio, then you can get more fat burning from your cardio and less lactic acid build up from your weight training, so less fatigue and soreness. If you do cardio first, you won't get as much fat burning from your cardio, will already be slightly depleted in your glycogen when you finally get to weight training so you'll have less energy for the movements, plus you'll have more lactic acid build up leading to fatigue and muscle soreness.

Cardio for three days then weight you don't want to build to many muscle it's hard to lose weight

Uh.... what..???

I would do Cardio for three days then weights you don't want to build to many muscles it's hard to lose the weight

Again, uh what?

if your goals are say, endurance training related, then it's best to do them different days.

If your goals are just to lose body fat, then it's always barbells before bikes. If you are tired out from cardio before you even start lifting, your lifts will suffer. Honestly, when on a deficit, it's better to look at cardio as an optional extra. Sure, it helps you burn extra calories (meaning you can eat more) but lifting on a deficit is stressful enough. Too much cardio can make you over tired, really hungry and can lead to insomnia and just a feeling of having "run out of gas"