Unable to drag and drop footage in Final Cut Pro

FCPX has been like this from day one, I get this a lot, also. When you click-drag on a clip in the Browser, FCPX assumes you're selecting a range, by default. You have to click once to select the clip. Then you can easily click-drag to the timeline. Something I've complained about for a long time. But yes, learn the editing keyboard shortcuts like Luis says, that's faster and easier and avoids this glitchy FCPX behavior.

I guess that this depends on how you drag, since dragging can do both things.

Drag horizontally to select a range, drag vertically to actually drag a clip.

Also: it helps to learn a few keyboard shortcuts, like E to appEnd to the timeline; also press X if you want to select the whole clip.

If you are starting with FCP, it is helpful to take some time and learn by following these free courses from two great teachers:

Steve Martin (of rippletraining): Learn FCP in Under 60 Minutes - YouTube

Izzy Hyman (of izzyvideo): Final Cut Pro Tutorial | Izzy Video

If you switch to list view, you can drag the clip from the list into the timeline. If you're in filmstrip view when you mouse down on the clip it will select the clip. Yes, something has to be selected.

Are you trying to drag the whole clip or part of the clip? What are you doing? If you want the whole clip and mousing down on the clip selects, what does it matter that a yellow box appears around it.

What are you trying to drag? The whole clip? As Luis said, press X to select the entire clip and then drag it to the timeline or use the appropriate single letter keyboard shortcut.