In every application, in the Configuration tab is a setting called Require Login which is set to No by default. If it is set to Yes then the user will be required to login when they first access the application.
However, if your application isn't configured to require login, by default users will be logged in as the system administrator, as defined in the Application record. If, instead, you want to allow users access without logging in but don't want to give them full, administrator access, you should define a guest account.
To create a guest account, simply create a user record with the name 'Guest' (the actual name doesn't matter). When creating the record, set the 'Guest' field to 'Yes'. Only one user can have the Guest login set.
Now, when users access the application they will automatically be logged in as that guest user. Any roles defined on that user record will also be applied to the guest user access.
If the user wants to access the system under a different account, they can simply click the "Sign Out" link on the top right of the application and this will take them to the login.aspx page where they can enter their alternative credentials. To go back in as guest, they would simply click Sign Out and then close the window and go back in to the application again.
Be very careful when setting up the guest account to ensure they do not have unexpected permissions. You should review the security section thoroughly and test the account before setting it as the guest account.
Next Topic: Creating Users
Please post all questions on the support forum. Thank you.