Ford transmission only shifts into gear when engine is warm. What's that mean?

Ford transmission only shifts into gear when engine is warm. What's that mean? - 1

Added (1). but shifts into reverse just fine

Check the fluid level, if its full, the only advice i can give is to take it to a trans shop

It's what a former mechanic of mine referred to as "morning sickness". Unfortunately the problem will become worse and worse until it doesn't work at all. So if it's worth it to you, get the transmission rebuilt. If not, start looking for another car.

Needs rebuilt. What's happening is rubber lips seals inside the transmission are worn. Once fluid warms up it expands the rubber allowing the pistons to apply. Reverse works great since pressure in reverse is higher than forward gears

Sounds like the transmission oil pump is failing. There's not enough pressure to lock the clutch packs while cold. You will be needing a tranny soon. It's time to trade the vehicle in while it still moves or plan on spending $2,000 to rebuild the transmission. It won't last long at this point.

While it very well COULD need to have the transmission rebuilt, it may just be low on oil. Check that first.

This is, however, assuming that it's an automatic.