I have been learning to use Rational Rose Enterprise methodology RUP - UML, I heard that is the most basic one to use. I also know how to use IBM Architect, but I am new to it. My question is, to diagram a website such as a social network, (Facebook, twitter, etc...) or a complex website, (eBay, olx, etc...) which methodology should I use and which software should I use? I am new to this and any help will be useful.
If you have any websites or books you can recommend it will be helpful.
Is this even possible?
Any UML tool will help you to build an UML model, which is a software representation. It is up to you to find the right tool. A stackoverflow exchange on the topic exists (event if this is considered non constructive).
It is very difficult to make any recommendation. It depends on what you wish to model. It will be difficult to represent properly a web application on the hypertext point of view.
In UML, a hypertext document is an artifact. This is an UML element which is not specific to hypertext documents. Therefore hyperlinks in the UML world would be traditional UML associations (dependency, composition, etc.).
There is a non-standard solution for modeling hypertext applications: the hypertext model in WebML. That language is progressively standardized in the frame of the OMG with the IFML language. However, as far as I know, the hypertext model is not part of the standard until now. And the support of IFML is quite rare.