They can be an asset or a major threat to your safety, depending on how you understand them. As broken waves wash toward shore, they carry a lot of water with them. The water pools up next to the beach and forms a longshore current on the inside. As the water moves up or down the beach, it will often funnel back out to sea in the deeper spots. This swift current goes straight out through the surf zone and dissipates once it's beyond the break.
Rip currents are easy to spot.
Because they're in deeper water, there are usually no waves breaking in rips. The best way to get out of a rip is to swim up or down the beach, parallel to shore. If this still doesn't free you up, and you feel like you won't be able to get back to shore on your own, remember that the universal distress signal is the waving of one arm. They have a direct effect on how waves break. During low tide, you may be subject to exposed rocks or reefs that weren't there six hours before.