Well if your control is in N, engine off, and you can spin the prop freely, you are half way there. If you shift into F gear and the prop resists turning CCW viewed from the rear but ratchets as it turns CW you have it right. Don't shift into R without the engine running or somebody turning the prop while moving the shift lever, but if you do it resists turning in both directions as it doesn't have the over run clutch function like F geart. There are vertical sided cogs and slots that have to line up before the shift mechanism will fully engage R gear.