1. To secure oneself into something with a strap, harness, or seat belt. I just need to strap into my seat before you start driving. We all began strapping into the cars of the roller coaster, nervous and excited in equal measure.

2. To secure someone or something to or into something with a strap, harness, or seat belt. In this usage, a noun or pronoun is used between "strap" or "in." Make sure you strap the kids into their car seats properly. He didn't strap the cargo into its place securely, and it ended up falling over and breaking in transit.