Groups x trust levels

I have 8 groups in my community - admin, moderator, staff and other 5 groups that are the trust levels (0,1,2,3,4).

I have 22 people in my community but I dont know why all of them are in group of trust level 0 and 1. But they shouldn’t be just in 0? Because almost all of them are new in the community.

I dont understand the relationship between the groups and the trust level… Because if my users are new they should be in the level 0, but they are all in the group 0 and 1.

My idea is that the users will evolve as they interact and level up, but now they are all in the group of the trust level 0 and 1. I dont know why.