Who gives you multiball? If your coach, he/she will know what to do. If it's a buddy:
first get the basics right. USe a camera, from the beginning. Get 100-150 ball and make a ball picker. Change exercises per full sets (all the balls) and rest during picking up the balls. Since you are basically a beginner, do the basics. Simply loops against block, backspin with BH and FH, 1 FH, 1 BH. Check your technique with the camera and try to correct it constantly. I am sure you can figure out basic exercises. What's important is to rotate the basic drills. That means you NEVER want to practice the same element twice in a row. After 1 set of FH loops against backspin, the next set you do sthing different. That is because you want to improve in the long term. There is a curve how effective the learning process as the time goes. Basically, a second set would be a waste of time. You want to ROTATE. SO always do more sets of the same or similar drills, but do something else between them.
Don't forget the camera! Upload the videos here, so we can help what you should correct in your technique!