Well you asked for it. For just starting out there are a couple of ways to go. First suggestion is to look for a white ash tree that is straight and without limbs for or swirls on the trunk for about 6 or 7 feet. It is best if it is from 8 to 12 inches in diameter and it must be green and growing ( not already standing dead). Now is a pretty good time to harvest, except it will be hotter than haddes in the timber, but the sap will still be up in the tree. Cut the tree down and remove the log section that you have chosen. If you can it is best to split the log right then, depending on the size, into quarters or eights. You want splits that will give you a piece with the bark on that is about 3 inches wide and about 7 feet long or more. Now load it up and take it home and when you get there start peeling the bark off. Just start something like a knife under the bark at one end and then just peel it off as one piece and leave the brown inner bark alone for now. Now if you want you can put thin glue or varnish or shellac or something on the ends of the log to help seal it to make the moisture migrate out of the wood grain itself rather than just down to the ends like a straw. One reason to make the splits extra long is there will be room to cut off any cracks or splits that may occur near the ends of the logs so this sealing isn't really necessary it you have made them long enough. Last part of this prep work is to put these splits or staves up in the rafters of your garage to season and dry for several weeks. If you can it is best to arrange them with the split wedge side down so that as they dry they will take a little natural deflex set that will help later down the road. Hot and humid weather isn't the best for this drying, but the rafters will be hot and pretty dry. This will take from 4 or 5 weeks to 3 months depending. It is best to have a moisture content that is 7 or 8 per cent. Dryer than that the wood becomes very brittle and wetter it will take too much set and not be very elastic.
The other thing you can do is go to a lumber yard and get a very good quarter sawn board of hickory or ash and start there, but be advised you will probably want to back any bow made this way with something like rawhide or linen, or nylon. For now completely forget about sinew backing because that gets pretty detailed and messy.
If you can find a copy of the Traditional Bowyers Bible I then buy it and read it while you are waiting for the staves to dry. Read and try to understand it before you touch you wood again. It will have basic lay out designs that will help you decide what style of bow you want and how you want to proceed.
Some general equipment you should have are a chock line, a square, a yard stick with a straight edge, a draw knife, maybe a spoke shave, several files and wood rasps, a 5/32 chain saw file, a hand plane of Stanley Surform, a good bench vice or wood worker vice, a tillering string and a tillering board. A band saw for roughing out the rough shape is also very helpful as is a palm held sander when you get to the finish part and a bow scale to help adjust draw weight. As you are building you bow try to never draw it futher than the target draw weight. That means that if you want a 50lb bow never draw it futher than what 50 pounds is. At first that might be just 7 or 8 inches and you progress it will go to 18 inches and then hopefully up to 28 inches. Also remember to leave it a little heavy as it will loose some draw weight as you sand it and shoot it in.
Read about woods and tillering an shapes before you start to have a better idea of what you want to do. Keep a couple of extra staves because it is more than likely that the first one won't live clear through the process or that it won't turn out as you hope it will, so you can start over with out having to harvest and dry more wood. :way:
Also when you show off your new bow some buddy is going to want one too so you have wood to do extras. Then just hold on and enjoy and ten years from now you can look back and see that you have made 300 or 400 bows and still haven't come up with the perfect one so you just keep trying. We can post more when you get to the proper stages but for now just absorb.