Counter

To insert a page counter for the page itself you are inserting it on you can simply insert {{Counter}}, this inserts Template:Counter (only works on regular article pages, sets namespace to 0).

Hits on Counter
<counter></counter>

To insert a counter for any different page, including Talk pages, User pages and all other namespaces, you need to specifiy page name AND page namespace, use this syntax:

<counter>namespace=0&page=Sandbox</counter>

Examples:

Hits on Sandbox: <counter>namespace=0&page=Sandbox</counter> (namespace 0)

Hits on Talk:Sandbox: <counter>namespace=1&page=Sandbox</counter> (namespace 1)

Hits on User:mutante: <counter>namespace=2&page=mutante</counter> (namespace 2)

Hits on User_talk:mutante: <counter>namespace=3&page=mutante</counter> (namespace 3)

Here you can find a list of the Mediawiki_Namespaces and the numbers they use.