Install the Technic launcher

In case you haven't already, download the Technic launcher. This is required for Tekxit. You will be asked to sign in using your Mojang account.

Begin Tekxit installation through the Technic Launcher

Once the Technic launcher is downloaded and installed, click the "modpacks" tab at the top of the application window. You will then click the search bar titled "Add pack or search" and type in "Tekxit 3". You should see a listing for "Tekxit 3 (official) 1.12.2" by Slayer5934. Select that modpack and click the "install" button at the bottom right.

Get Fancy

If the modpack downloads quickly, or you're willing to wait an hour or two, great! You're done. If the modpack takes a very long time to install, it's time to get a little fancy. Cancel the modpack download by clicking "cancel" in the bottom right corner of the Technic launcher, then manually download the modpack files stored on this server and save them to your computer's downloads folder. Back in the Technic launcher, click the "Modpack Options" button in the top right corner and then select the "open" option next to the install folder path. Once opened, browse to the "cache" folder and paste the downloaded .zip file (still compressed) into that cache folder.

Almost done!

With that .zip folder added to the cache folder, back in the Technic launcher, click the "install" button again and it'll install the pack within a couple minutes while using the .zip file you pasted into the cache folder. Once the install is complete, click the "play" button in the bottom right corner and start playing!

Does Java whine at you?

If you start the modpack and Java yells at you saying that it doesn't have enough RAM, close the error window and return to the Technic launcher. In the top right corner, click the "launcher options" button. In the window that appears, select the "Java Settings" tab and set the "Memory" option to at least 3GB. If you don't have 64 bit Java installed, it will not allow you to go past 1.5GB. In that case, you should download 64 bit java from Oracle's website. Make sure you choose the "Windows Offline (64 bit)" option in the downloads section (or whichever 64 bit version is applicable to your system). Once 64 bit Java is downloaded and installed, close and re-open the Technic launcher and repeat the process of increasing the Memory setting to at least 3GB.