How to check exactly what apt install [some package] is going to do?

Simulate the results of installing a package without actually installing it. Open the terminal and type:

apt install --simulate package-name

Results

• The following additional packages will be installed:
• Suggested packages:
• The following NEW packages will be installed:
• X upgraded, X newly installed, X to remove and X not upgraded. The X's are replaced by numbers. Example: 0 upgraded, 99 newly installed, 0 to remove and 6 not upgraded.
• Inst - indicates packages that will be installed (99 lines in the above example, one package on each line)
• Conf - indicates packages that will be configured