If you try accessing Teams the many ways you already know to access Teams, by going to Teams.microsoft.com or using e-mail links to a Team etc. and you log in with your Personal MSA account, if that account is a guest of another Team, it will take you to your last logged in tenant or only tenant that you are a member of. You will be shown as a guest there and all is fine. But if you want to go to or setup "Your" instance, you don't have an option to create one from there and your kind of in limbo.
I searched around twitter verse and found links to some sites about free Teams and what not but I really wasn't finding the answer. Poked around the office.com pages etc. and had no luck. I ended up taking another MSA account that I had as a guest of a test tenant, and left the tenant as a guest so the account was no longer tied to any other tenants and then I was presented the sign up link for Teams.
Turns out, all you need to do is go to here: https://products.office.com/en-US/microsoft-teams/free to sign your account up for Teams. It would be nice if this option was available to users that default to guest Teams and haven't set this up yet. But hopefully you guys find this post and save yourself some search time!
The sign up process from there is pretty straight forward. Asking for some basic information, make sure your business name is the name you want your Teams tenant to be called as it uses this field to create that namespace. Once completed give it a minute before clicking lets go as the creation process takes a little longer on the back end, or it will end up putting you in your guest Tenant and You'll have to refresh your page and then choose it out of the tenant picker in the top right corner to get to your new tenant.