As Pilou points out, there are lots of tools to use and which one you need will depend on what you are modelling - or what part of a model you are working on.
Your best bet would be to follow a tutorial such as Marian's car thread:
viewtopic.php?f=335&t=37611&hilit=tutorial+marian#p331991
Alternatively, pick a subject to model, open a WIP thread and then ask questions about how to model specific elements.