Once logged in add items by PMID by visiting: http://tools.wmflabs.org/fatameh/pmid/add/*Your PMID*
You can use the same type of URL to add items by PMCID: http://tools.wmflabs.org/fatameh/pmc/add/*Your PMCID*
Alternatively you can use this form to add by PMID (it just goes to the url)
If you want to batch add items then you may want to use fatemeh form the commandline or an application other than the browser. To do this you need to make a GET request to the same urls prefixed by '/token/'. You also need to set the HTTP Authorization Header to 'Token < my token >'. You can your token on the login page. Obviously whoever has this token can add items with as your user so keep this secret.
For example to do this with cURL you may run: curl --header "Authorization: Token mysupersecrettoken123456" tools.wmflabs.org/fatameh/token/pmc/add/PMC987654
For more information see the documentation here: https://www.wikidata.org/wiki/Wikidata:WikiProject_Source_MetaData/fatameh