Actually, your weight is simply an energy balance. If you input (eat) more and output (workout) less.....then you grow fat lor. The scientific equation would be:
Excess Energy = Food/Beverage energy - energy burnt - energy in your sai.

So hor....to decrease excess energy, you have to:
- eat less
- workout more
- increase energy contained in your sai

The only way to increase energy contained in your sai is to lao sai more often (so that your body doesn't absorb so much of what you ate)....but this is really really not a good idea, so please don't try it.

Getting fit/conditioned is a trickier matter than balancing one's weight. For this, you need to workout to make the muscles "harder" to give that toned feeling. While its not impossible to tone up certain parts of the body only, its more realistic and practical to tone up the whole body.
If you don't have time and only can do one kind of exercise, then the aerobic sort would be the best choice (dancing, skipping, jogging, brisk walking, aerobics, etc.). I say best choice because it works out the whole body and especially the heart.
The downtown gyms are not cheap....and the entrance fees are not the end of the total costs either. Only join if you wanna be "in the scene". Otherwise, just pay a few dollars to get into one of those state-run clubFITT gyms (like those at CCs).
And realise that exercise is usually effective only if done on a regular, constant basis.