When you have found a server that interests you note down the IP Address and Port of the server and then start Minecraft and click 'Direct Connect' and input the IP and Port. Alternately, if the server does not show their IP Address and Port you can enter their connect address (subdomain.domain.com) instead.
Can I Connect Minecraft PE to a PC Minecraft Server?
No. The Pocket Edition of Minecraft and PC Mineraft are not the same game, both have different features which means they are not compatible. However, PC Minecraft players can run a server on their computer that Pocket Edition players can connect to if they install PocketMine software.
The video below will show you how to join Multiplayer servers In Minecraft PE