1 tbs (9 g) in the loose form per meal, two meals a day, with plenty of water or fluids. It’s 30 kcal per 1 tbs. I try not to rely on it, but if I don’t meet my 25 g of fibre a day, I supplement with psyllium husk.
With psyllium husk, start with a smaller dose, maybe like 1/2 teaspoon, and gradually increase the dose until you get the effect you want. Too much suddenly might cause digestive rebellion (sudden increase of fiber). Different people will require different amounts. The package will usually indicate the common daily dosage, 1 tablespoon I think. And not taking it with enough water could cause constipation (collects into more of a hard lump rather than a diluted gel).