Hello Abdul,
1. Consume an external web service (Outside company network) from SAP PI
While consuming external webservice ensure any certificates are required. Also check for firewall/port settings which needs to be opened from PI to send data to webservice. Performance depends on the size and amount of data going to be triggered.
2. Provide Web service from SAP to an outside company through SAP PI.
This is should be a bit simple. Generate structure and share the WSDL and PI endpoints to the External system(who is going to consume services).Ensure all settings mentioned are open from PI so that data can be triggered to PI.
Below link should give you some more idea on configuration part.
**************** - WebService to WebService Synchronous scenario
Developing and Configuring Web Service Scenarios - SAP NetWeaver Process Integration - SAP Library
SAP Web services performance tuning in terms of concurrent users?