As you continue to do more and more collaborating in Teams, using, sharing and finding files becomes more important. Initially, you can recall where you saved or used the file but as your Teams increase and you have more and more files - you won't be able to rely on your memory. It's important to know and understand how Teams organizes your files and the best way to find them. You also want to be clear on file permissions.
If you want to save and share files in Teams, you need to use OneDrive. Without going into a lot of detail, this provides the cloud platform for making these files accessible to everyone on their phone, tablet and laptop apps. Talk to your IT department if you have questions about OneDrive and/or setting it up.
In the "old days" of networks and folders - you would organize and store your files by creating a nested file folder structure. Client Files > Client A > Marketing might be a folder structure with nested folders.
The best way to share and organize files is to use Teams and Channels. This creates a file structure for finding and saving files. This also allows you to give all team members access to the files.
If you want to just upload the file to the files area of the channel, this is similar to saving it to a folder. Everyone who has access to the channel will also have access to the file and see it listed.
If you need to share a file with just one or two others and not an entire team - you can do that via chat.
File sharing is so important to Teams that it's a main tab on the shortcut bar. When you want to see all your recent files, search for a file this is great place to have a high level view of all the files you have in Teams.
As you continue to use Teams more and more, you will have many files and organizing and finding and organizing files will be more important. These pointers will help you understand the framework for how files are organized in Teams.