A more thorough explanation:

Summary (adjective) means short and concise. For example, a summary account of a book or movie would give a brief overview of the main points without going into too much detail.

It can also mean without the usual formalities, such as a summary trial where a judge makes a decision without a jury.

Additionally, it can mean immediate and done without delay. For instance, if a new weapon is put to summary use by the military, it means they started using it right away without waiting for further instructions.

Summarily (adverb) is the adverb form of summary.

Summary (noun) can also mean an abridgment or brief, like a summary of a long report or article. It can also refer to a short application to a court without the formality of a full proceeding.

For example, if someone wants to file a summary judgment, they can ask the court to make a decision without going through a full trial.