Go to Restrictions > No Through Roads 
You can set a link or links to be considered as no through roads. That is a link where a route can be start or finish but it cannot be complete traversed.
This tool will change the attribute column in the network table.
Click the "No Through Roads" option and then click on the link. If you have the Show Restrictions on then you will see a no though roads symbol on the map.
You should note that the restriction is applied to the whole link and not just the place that you clicked.
The restriction is NOT applied immediately, but they are only applied to the network, if you save the restrictions.