Step 1: Install either Firefox or Chrome (if you haven’t already done so).
Step 2: Install the LeechBlock extension:
Step 3: Click the LeechBlock button 
and select Options.
Step 4: Specify which sites to block and when.
That’s it! You’re good to go.
Visit the examples page for some examples to illustrate the different settings or visit the FAQ page for answers to some frequently asked questions. Note that there’s also a community support forum.