There are multiple configurations that solar panels can be wired in. These include multiple panels in series, in parallel or a combination of both. When wiring panels make sure the panels are exactly the same otherwise you will create an inefficient system

Below are some common configurations.

You can buy the parts required for parallel connections here 

1) Connecting two solar panels in series

2) Connecting two solar panels in parallel.

3) Two panels in Series in parallel with another two panels in series.