Here are some tips, if you've never worked the scorekeeper table in filling out the scoresheet:
1) Plan for a parent to sit with you and walk you through it the first time
2) Read through this presentation, downloaded from the VolleyballAlberta.ca site:
The presentation is quite detailed (108 pages), it is recommended you read through the entire thing. Consider re-reading the section on keeping score and substitutions, pages 24-42.
3) Don't be intimidated; you'll get into the flow once the game starts.
Tip: Look at the ref, then mark the point. Don't mark the point and then look up to confirm if you're correct. The problem is, you'll miss what side the ref indicated and also you may be wrong about who got the point and that will mess up your pristine scoresheet :)
Other downloads that may help:
filled out scoresheet with extra notes
filled out scoresheet without the extra notes