Tener ganas means to feel like (smth) and querer simply means want. Tengo ganas must be followed by an infinitive verb. So you can say "quiero comida" (I want food) but you can't say "tengo ganas de comida", you must say "tengo ganas de comer" (I feel like eating)

Tengo ganas = feel like (+ verb) -> I feel like going for a walk querer = want -> I want to go for a walk