When I use the graph explorer (https://developer.microsoft.com/en-us/graph/graph-explorer) to call graph API (like teams api), it automatically provides me with an access token which has the permissions and authentication to do tasks (such as creating a team and adding people).
However, when I try to search for a way to get a access token (https://learn.microsoft.com/en-us/graph/auth-v2-user), it seems to be the case that I would have to register an app with Azure AD (which to begin with only has Read permissions and would not allow me to create teams for example), and follow more steps to get an access token.
My questions is, why is this the case that the access token that is provided through graph explorer lets me do everything while I have to go through so many more steps to get a token by myself (such as creating an app, requesting permissions, and then getting the token). Or is there a simpler way to get access to the access token (with me as the user) that I am not aware of to use graph API?
That's because Graph Explorer is also registered as an application and exists as a service principal/enterprise application in your Azure AD tenant.
Every single application that gets tokens from Azure AD must be registered as an app somewhere. In case of multi-tenant applications like Graph Explorer, it is registered in one tenant and a local representation of the app (a service principal) is created when the first user consents to permissions required by the app. (or it exists by default, some Microsoft apps exist in every tenant at creation time)