Important takeaway for any beginner is that there's not one specific right answer in the world of leaders and tippets.
If the question is "what works?" given a set of parameters (fly size, general expected catch, rigging/type of fly or flies, etc.), there's usually a decently broad range of specific setups that will work well enough.
When I was just starting out, the biggest thing I had to learn to account for in my leaders & tippets was that the leader isn't just there to get your fly away from your fly line, it plays an essential part in the cast as well, and heavier material will transfer the energy of the cast better.
For specifics, if you're stating out with a normal length med-fast 5wt, I'd say grab yourself 4 leaders at 7.5 ft 2X and two at 9 ft 3X. All mono for now.
When you get them home, take them out of the bag and uncoil them, and use a Sharpie to mark a point approx. 18" up from the tip. Doesn't have to be exact, you just need a reference point because it's a lot tougher to tell where "18 inches from the bottom" is once you start clipping from the bottom. Mark them up, re-coil them, and go fish.
The 2X are your nymph & streamer leaders. Buggers, clousers, zonkers, etc. can be a bear to cast with a longer, lighter leader, so you're going to use the 7.5 ft 2X as the base for a short, stout leader. Generally you're fishing these flies for bigger, predatory fish, as well as bass and pike, so the fish you're after aren't leader-shy. Use two of the 2X leaders for streamer fishing, and when you get up to the Sharpie mark, tie a perfection loop into the bottom of the leader. This will allow you to add tippet as needed without continually eating away at your main leader. Just get a spool of 2X tippet, pull off 18-24", tie a perfection loop in one end, and do a loop-to-loop connection to the bottom of your leader. If you're fishing small versions of these flies (like a #12 bugger), you can add 18-24" of a finer tippet to the bottom of the normal tippet, with a surgeons knot.
For the second two 7.5 ft 2X, make those your nymphing leaders. Using either the full length or the trimmed back length, tie on about 2 feet of 2X or 3X tippet, and add the loop to the bottom of that. If you've got hi-vis line that you want to use as a sighter, this is the place for it (with the 18" trimmed back). Below the loop, you're going to add tippet based on how deep you're fishing, either in 3X or 4X, depending on conditions.
For the two 9 ft, 3X leaders, once you've marked them and fished back to the mark, tie the loop and use them for dries and small nymphs that you'll fish without much "rigging". You can hit these two leaders with the floatant of your choice to improve performance, too.
