You can share files in Easy Teams in chat channels or in directchats.
Share the file by dragging it from your computer and dropping it into the chat channel.
Tap the plus sign in the chat compose and select Share files. Select the file you want to share and press enter.
When you are going to share a file from Dropbox for the first time, you need to log in. After logging in, you will see the dialog where you can select the file to share.