There are two ways of finding systematic reviews using PubMed to do so. One method searches for subject-related information, and then applies the Systematic Reviews filter from the filter list on the left hand side of the screen. The second method uses Clinical Queries to locate systematic reviews, then applies other filters if necessary.
Note that PubMed locates systematic reviews from the Cochrane Database of Systematic Reviews as well as from core journals in specific fields.
The Sytematic Reviews filter on PubMed will include meta-analyses. If however, you wish to search for meta-analyses on their own, use the Meta-Analysis filter under Article Types. You will need to deselect everything in this filter except meta-analyses.
When you select the Systematic Review filter on PubMed, this filter is mapped to an extremely sophisticated search strategy. Click on the link below to view this search strategy. However, you will not need to remember this search strategy, because it is already "hedged" for you, ie. PubMed does all the necessary work in the background on your behalf.