Sync Macbook with imac

There are several options:

• Apple's iCloud Drive seems tailor made for this. You should investigate how it works carefully (Apple has thorough online documentation about how iCloud Drive works, for instance Work with folders and files in iCloud Drive - Apple Support). Basically, folders like your Documents folder, Desktop folder are stored online and a copy of them is downloaded to each of your devices signed in. So this ensures that those folders are immediately identical on all your Macs and devices. Changes in a folder on one device are immediately mirrored to other devices.
• You can also use iCloud to synchronize other things like Pictures, email, etc.
• There are other similar tools offered by Dropbox, Google, Microsoft.

Another option is to use a tool like Chronosync.

You can even do it in a low tech way by using a portable external drive that you shuttle back and forth and use to copy changed files and folders. But that requires manual effort. But you don't have to install anything.