Do you want to do multiple tag/category queries in WordPress by URL?
Use , (Comma) for OR operation
Use + (Plus) for AND operation
Suppose to get all posts tagged css or jquery then:
https://techbrij.com/tag/css,jquery
To get all posts tagged css and jquery
https://techbrij.com/tag/css+jquery
For those of you not using “pretty” permalinks, then it would be:
http://mywebsite.com/?tag=tag1,tag2 http://mywebsite.com/?tag=tag1+tag2