Here's a little step-by-step guide on how to join our modded Minecraft server. I wrote it to be as clear as possible for the sake of avoiding confusion.
1) Start by downloading the Technic Launcher here. Just choose the download for your system at the bottom of the page.
2) Launch the TechnicLauncher.exe you just downloaded and click install.
3) It will automatically launch when done installing, however to launch it in the future you just have to run the TechnicLauncher.exe again.
4) Log in with your Minecraft account.
5) Click the "MODPACKS" at the top and choose "Tekkit Legends" on the left. Click install in the bottom right.
6) When it's done you can click "Play" which is also located in the bottom right.
7) Once you're at the title menu, click "Multiplayer" and "Add server" - give it whatever server name you want. The server address is 220.127.116.11:25575
Keep in mind the amount of content can be overwhelming. Personally I recommend that if you're overwhelmed, watching a let's play or something similar should help you start out. Of course you can always ask other players on the server as well.