Firstly make sure that your composite decking is properly cut according to the length.
Then take a piece of composite decking and put it on the beam or joist and make sure that the piece of decking is aligned with the edge.
Next take the drill machine and bore two holes with it at the point of each crossing joist. Make sure that the hole you drill is about 1 ½" to 2" in depth.
Once you are done making the holes, the next step is to insert the screws into the holes that you have just drilled. Once you insert the screws tighten them with the drill machine and check to make sure that these are also holding the joists below.
After that take the other piece of your composite decking and put it along side the first piece of decking that you have just joined with the joists.
Keep on joining the pieces of the composite decking with the joist in the same manner till all the pieces are joined together.