After the download, extract the contents of the zip-File to your desired location, open the Launcher and configure everything to your needs. When you see the main window, proceed with the next step.
call_receivedImport the Modpack
Click on "Add Instance" in the top left corner.
As a name, you can type in anything. I would recommend "Hexxit Ultimate".
You can leave the Group empty, if you want.
On the left side, click on "Import from zip".
Click on "Browse".
Choose the zip file, which you have downloaded in the beginning (HexxitUltimate.zip) and click on "Open".
Click on "OK" and wait for the Progress Bar to finish.
updateCheck for Updates
You should do this step everytime you want to play the Modpack.
In MultiMC, select the Modpack and click on "Minecraft Folder" on the right side.
Double-click the "HexxitUltimatePatcher.jar". A little window should be opened now.
If it found some updates, click on "Apply Patches" and wait for the Patcher to finish patching.
When it is finished, you can close the Patcher.
play_arrowPlay the Game
In MultiMC, just double-click the Modpack and you can start playing right away.