This mission begins at Floyd's place, who happens to be Wade's cousin. Trevor is looking for something to steal and since Floyd works at the docks, he's hoping to get some inside information. Get in the vehicle and drive to Pier 400. Once you get there, park inside and go to dispatch.
Follow Floyd until you get called to get into Dock Handler to move some containers (get into it like any other vehicle). Maneuver the container handler with up and down on the left stick and use right on the directional pad to pick up a container. You need to move the handler over the container, lower it over on top of the container and then pick it up. Move it into the designated area and release it with the same button you used to pick it up, then do the same with the other.
Once you get both containers, head over to the crane and climb your way to the top. Now, you will have to do some work with the crane. Move the cabin with the right stick and the spreader with the left stick. You need to move it so the spreader is lined up over a container, drop it and then pick up the container. Go to the other end and place the container onto the truck, then do the same with the second container.
After you're finished, climb to the top of the crane and go to the end of the balcony. Take out your phone and take the pictures of the freighter that you are asked to take. Once you're done, go back to ground level and get into the big rig. Drive it to the other dock and after the scene, get back to Floyd's apartment. Now, you will need to choose an approach for the next heist, either the Freight or the Offshore.