Spiders normally use their silk to make structures, either for protection for their offspring, or for predation on other creatures. They can also suspend themselves using their silk, normally for the same reasons.
The trapdoor spider will burrow into the ground and weave a trapdoor-like structure with spindles around so it can tell when prey arrives and take it by surprise.
Many small spiders use silk threads for ballooning. They extrude several threads into the air and let themselves become carried away with upward winds. Although most rides will end a few meters later, it seems to be a common way for spiders to invade islands. Many sailors have reported that spiders have been caught in their ship’s sails, even when far from land.