Really simple way to get started.
1) Get the latest version of the Tekkit Client from the Tekkit Website on the left hand side of the page, they list the latest versions of Java and the latest version of the installer.
2) Open the launcher. It looks similar to the vanilla client, put in your username and password but don’t quite connect yet!
3) Select ‘Tekkit’ from the dropdown list in the top-left of the launcher screen. You’ll see there are a few different packs of mods! Have a play with them on SSP but for Archetype, you’ll need to run Tekkit.
4) Login. The installer will take care of adding all the mods.
5) If that all went well, get ready to connect!