You go to the store and buy a roll of string, then a package of chicken necks, Buy 1 ounce lead pyramid sinkers and attach sinker to the bottom of an 8+ foot piece of string. Tie a chicken neck above the sinker. Buy a crab net to catch the crab while he is chewing on your chicken neck. Some stores sell "crabbing" rigs complete.
Walk out onto the jetty. Find a place where you can get down on the rocks close to the water. Drop the string in the water and WAIT. When the crab bites, you'll feel it. Pull the string up slowly, have the net ready, and bingo, you have caught a crab. If you catch a lot of crabs, and you want to eat them, I am attaching a file (Click) that tells you how to clean them.
Take the center road of Singing Sands North. Crabbing on the Intracoastal there. Also go down Stingaree road toward the Bay. Take the left fork and crab along that canal there. To go crabbing in Texas, you have to have a fishing license and a salt water stamp.
P.S. Be sure you have a bucket to put the crabs in!
More about Crabs
How to Clean a Crab: Click Here