PubMed Search Builder
Within NCBI's MeSH Database, you can search for and add MeSH terms to the PubMed Search Builder on the right side of the page.
MeSH and Boolean Operators:
When you find an appropriate term, you can add it to the search builder, linking MeSH terms with Boolean Operators. You can continue searching for and adding to the builder which saves the string as you go. Select "Search PubMed" when you have added all your desired MeSH terms.