Hey @jullia , thanks for reaching out to the Dropbox Community.
You can see how much Dropbox space you're using, in the plan tab of your account settings.
The free version of Dropbox offers 2 GB of space + any bonus space you have earned.
If you're using more than that, you won't lose your files, but syncing will stop for your account and you won't be able to add new files.
I hope this helps, but let me know if you have any questions!