When you put "uid","xxxx","password","xxxx","signform","signin" into Post Data filed it will automatically transform to "uid=xxxx&password=xxxx&signform=signin" with Content Type set to urlencode, which is default
For your second question read this post from @Fox ,
maybe its what you need. Its in Russian, but you can
use translator. There is an example script too >
Each asynchronous function started, starts in separate thread.
So in that example you will have 2 threads since 2 asynchronous functions
will be started, each with its own (different) script.