[quote=HollywoodMole]
Don't they have episodes that have been completely lost?
[/quote]

Yes. A good chunk of Hartnell's and Troughton's episodes, unfortunately. 

[i]However[/i], fan-made reconstructions exist for these episodes. They're rather impressive.

As for the episodes that Netflix doesn't have, you can find just about all of them on Dailymotion.

But in terms of just getting started, it doesn't really matter that so many chunks are missing. Just find a complete arc, watch that and see what you can find from there. Given the way that most of the arcs are so self-contained, you really can jump in at just about any one of them and still understand most, if not all of what's going on. And when you really think about it, a lot of new Who episodes are like that, too. 

As you may have noticed, I'm not nearly as pedantic about strictly watching all episodes in a series 100% in order as most fans of a series are. *shrugs* I can assure you that you can skip around some and be fine.

Just... wait to try watching the lost episodes until you get into Classic Who in general, assuming you do find something that hooks you. The reconstructions are nice and they're better than having nothing at all, but sometimes they can be a little tiring to slog through.