4 wheel drive

I have just purchased a 1988 c10 suburban w/ the 6.2 diesel. the truck is a manual 4 spd and has 4 wheel drive. There doesn't appear to be lock out hubs. Are these shift on the fly? I know that this is a newbie question, but I have no experience w/ 4 wheel drive and there was no manual w/ the truck. How do I engage the 4 wheel drive? Thanks in advance for the responses.

That year did have auto hubs standard. Most were replaced with manual locking hubs when the auto hubs quit working. After you shift to 4x4 the hubs should kick in and you will be in 4x4, when you shift back to 2wd you usually have to stop and back up to disengage the hubs. These really had lots of problems and I would recommend a good set of WARN hubs.