You dribble, catch the ball — and start dribbling again. That is illegal: once you catch it you have three steps and three seconds to pass or shoot, or the other team gets a free throw.
Every beginner knows the three-step rule after twenty minutes. What comes after it still costs the ball regularly: dribbling resets the count, but only once. Take the ball back into both hands after dribbling and the dribble is over — from then on you have three steps and three seconds before you must pass or shoot. Starting a second dribble is a double dribble and hands the opponent a free throw. The classic beginner error is not a rule error but a reflex: you get pressed, you pick the ball up, you see nobody free — and you carry on bouncing it out of sheer awkwardness. The fix is receiving with a plan: decide where the ball goes next before you collect it, instead of going looking afterwards.