Question about backing up after initial full backup

I did a complete backup of my hard drive (a full backup of files and directories as a simple copy). This was all a few weeks ago. I want to back up everything that has changed since then. Im not sure what a base is, but Im guessing its the backup I did a few weeks ago? If so, it wont let me select this as a “base”.

What steps do I need to take to back up all my information that has changed since the last simple copy backup that I made?

Thanks

Into CTM, baseline is the original state of the computer just AFTER you install CTM.
If you restore any snapshot, it will become the actual files in the disk.
If you want the last situation, backup your files of the current snapshot.

To do incremental backup of files, well, there are a lot of freeware tools that do that.
Consider PureSync for instance.