1. provide yourself or others with the equipment or information needed for something
arm yourself with facts and figures
If you are 'armed with' something, you have what is necessary to get a specific task done or to understand how something works. A politician might prepare for a debate armed with all the statistics they need; a candidate for an interview might be prepared by arming themselves with enough research about the company and the job to impress the employer, or a mechanic might arm themselves with all the tools necessary to fix a faulty machine or vehicle. Whatever is needed to get the job done or to perform something well, preparing yourself means that you are 'armed with' what it takes.