The first thing to do is roll out the underlayment pad. Connect the pieces together with wide, clear, plastic tape. How your outdoor deck boards connect depends on the brand you buy but they are all rather simple; most simply snap together. Remember to stagger the joints.
Wood plastic composite outdoor deck boards is a type of “floating floor”, meaning that it is all connected to itself but not to the house. With this in mind, leave 1/4” clearance at each wall. On the initial wall where you start, use spacers that you can pull out before installing the baseboards.
As you go along you will need to use your mallet and pull bar to snug things up. A few gentle taps will do.
Things will get tricky as you go through doorways; the manufacturer's instructions most likely will not tell you about this because it impedes sales to DIY'ers. In some circumstances the best solution is to use your utility knife to trim the snapping connections on the adjoining planks so that they can slide together. In this case, use a few drops of wood glue to keep them together.