Colloquially called steroids are really drugs that in the correct safe amounts allow you to achieve the effect we expect when training our body. The action consists primarily in the fact that we obtain strength, endurance and easier to absorb nutrients that are the building blocks of our body. Training without steroids is of course the most recommended, but then we only get the effect that after reaching a certain level does not lead to the values that we would like to achieve.
Remember that these steroids were once created to heal people, but by using doping in sport they have been included in the list of banned substances and therefore they cannot be bought like dietary supplements.
That steroids are similar to potency drugs, e.g. Viagra, which was really created to treat hypertension and its side effect was an intense, strong erection that became a remedy for erectile dysfunction.