This depends on your OS and customization.

If you have Windows it should start automaticly
If you have Ubuntu but did not configure an automatic start you should start it yourself.
Simply start your terminal and navigate to the folder where you've installed Odoo , then start it. This are the steps:
1. cd odoo/odoo-server/ (note: this is the path where you've installed your Odoo)
2. ./openerp-server
3. http://localhost:8069/

If you need an install / configuration guide check out this page https://www.odoo.com/forum/help-1/question/odoo-8-latest-version-install-step-by-step-63448#answer-63710

What if you are on a hosted server? What is the address you use in your borwser? 

Thx

If you installed everything properly locally, you should open your browser and go to localhost:8069