Complex Purchase orders in service procurement

Hello Experts,

I have recently started working on service procurement but my problem is that I can't find any user guide for this, all I found is  introduction & setups of complex PO's.

Does service procurement offers only complex purchase orders? Or it offers some other features too?

What type of services, we  purchase using complex purchase orders? is it related to construction and tendering of services and goods only?

In my understanding it is like tendering process in which: A company opens requisition publically (rfq) for purchase of goods/services (constructional, consultancy, labor services etc), supplier/contractor bids on it, and company issues work order(complex purchase order) to bid winner supplier. After the work confirmation provided by supplier, company issues payment amount to his invoice as per terms defined.