Continuing with further exploration of custom permission levels, I feel it is very important to create a Group to put users in specifically.  For example, you may have an Accounting team.  You want to make sure they all have equal rights to do things within their site collection. You have already created an “Accounting Team” permission level.  The next step is for a site administrator to create a new group with this specific access. 

Go to the same area for adding new users:  Site Actions >> Site Settings >> People and Groups.

Under the New dropdown, select New Group

Here you will have similar options you see elsewhere in MOSS or WSS 3.0.  You can name the group, give certain rights to viewing, and set permissions.

In the bottom section, select your custom Permission level you want for this group.

Click create and you now have a new group with the permission levels you set.  Add users to this group and you are finished.