F5 basic configuration help

That is pretty vague - do you have specific questions that you can outline? If you're looking for general LTM config and concepts, have you read the LTM Basics guide or other docs at the Knowledge Center? The Knowledge Center includes documents on other modules as well (APM, etc).

Sorry if my question is confusing, let me come clearly... I have an environment where F5 is acting as a default gateway for many services whereas for few services VIPs are configured. May I get configuration guidelines for such scenario.

I'm still not entirely clear on which part of the configuration you need. If you need information on configuring BIG-IP to 'route' traffic that doesn't match one of your specific virtual servers, take a look at K7595 which describes how to configure Forwarding IP virtual servers. The forwarding server can be configured to handle traffic destined for certain subnets (or even 0.0.0.0/0).

K7595 also has a section on Emulating stateless IP routing using the loose initiation/close options.

Per the order of precedence in K14800 your more-specific virtuals will be matched first assuming your forwarding IP virtuals are less-specific. So traffic to your configured services will match those first, and other traffic will be candidate to match your forwarding virtuals.

There may be other solutions available, such as simply using a SNAT for traffic that needs to traverse the BIG-IP. Depends on your requirements.