When your mail is migrated from Outlook to Google, all mail will be copied to your Gmail account, including any messages saved in folders and subfolders.
Gmail labels are used to organise messages in your Inbox. You can assign a single message to multiple labels and can choose to show labelled messages in your Inbox, or just in the label itself, similar to how messages show in a folder in Outlook.
In the screenshot on the right, labelled messages are showing in the Inbox:
You can also display labelled messages by clicking on the label on the left-hand side of the Gmail screen.
In the screenshot on the right, CRM Upgrade and Google Training are sub-labels of the Projects label.
When you first go into Gmail after your data has been migrated from Outlook, all of the messages that were stored in Outlook folders will be saved in Outlook labels with the same name, but the messages will also show in your Inbox. If you would prefer to move a message out of the Inbox and only show it when the relevant label is selected on the left-hand side of the screen, you can archive the message as follows:
Select all messages you wish to move out of the Inbox and into their labels
Click on the Archive button on the toolbar
Note: If you archive a message that hasn't been labelled, it will still be moved out the Inbox. You can find the message again by clicking on All Mail on the left-hand side of the screen.