Carrying capacity determines how much a character's equipment slows him down. Once your character is carrying 10x his Strength score, he becomes encumbered. Encumbered characters move at half speed, take disadvantage on Athletics, Acrobatics, and Stealth checks, and are considered flat-footed. Also, in the event of a strenuous task or after every 4 hours of overland travel, the GM may ask them to make a DC 15 Constitution Save or incur physical ability damage.
Your maximum carrying capacity is 15x your Strength score. You can still lift 2x this max load over your head (still counting all your gear) but you may only stumble around at a movement rate of 5 as a full round action. You may drag 5x your max load under favorable conditions.