Step 1:

Find the BizRP Contentpack Collection on the Workshop and make sure you are logged into Steam.

(If you are viewing this ingame, the Workshop will open itself.)

Steam Workshop

Step 2:

Hit the "Subscribe All" button as seen on the picture.

Steam Workshop

Step 3:

The contentpack will be downloaded automatically and you can disconnect from the server.

As soon as the download finishes you can reconnect and start playing.