OK... now I get it, but it doesnt work .)
My imported WSDL and XSD must be alright, because I copied it from a bpel project, which runs on my computer just well...
Now I :
1. added these lines to the WSDL
<plnk:partnerLinkType name="OneStringLinkType">
<plnk:role name="OneStringProvider" portType="wsdl:OneString"/>
<import location="OneStringService.wsdl" namespace="http://onestring.si/"/>
2. than went to BPEL where i added INVOKE. Went to detail, new global partner link and choose my OneStringLinkType (until now i always created a new one).
The problem now is that If I go to the new created link, there are NO methods/params under the OneStringProvider...(i saw that there are no methods when i chose the partner link type earlier too)
Like it doesnt find any from the partners wsdl ...