Why you should use it, and how
Ravelry features, the Stash page is probably the one that meets with the most resistance from users. Which is totally understandable, believe me! I get it. But it is also incredibly useful.
About once a year I have a knitter message me on Ravelry, asking about a yarn in my stash. If you run out of a skein of yarn X in dye lot Y, you can search Ravelry to find who has it in their queue. If you're willing to help a knitter out (and lighten your stash), this feature is great!
What DO I Have?
If you have ever re-bought the same yarn more than once because you forgot you had some already, raise your hand! I have yarn that I NEVER remember that I have. I only remember it when I'm browsing through my own Stash page. "Oh yeah! I forgot about that stuff!"
"Shop The Stash First"
If you are trying to destash, you have probably heard this nugget of wisdom. Well let me tell you, it's a lot easier to shop your stash by scrolling down on Ravelry than by actually dragging everything out and digging through it.
When you go stash diving in person, the lighting is never very good, and there's always something that escapes your notice. It may be a skein of sock yarn that slips into the bottom of the Bulky container, or multiple skeins of the same yarn that you accidentally only count once.
It's also less overwhelming to look at everything on Ravelry. The computer screen gives you a level of abstraction that makes it easier to breathe.
How Much Do I Have?
Click the green Excel icon. Click to sum up the "Total Yards" column. Presto: the precise amount of yarn you have on hand, precise to the very yard!
Adding Your Stash
The best way to add your yarn to your stash is the "quick and dirty" method. You don't even have to bother taking photographs. Just go through your yarn tubs one at a time, and add all the skeins to Ravelry. Just the make, model, yardage, color, and dye lot. It goes surprisingly quickly!
You can go back and photograph everything later. You can also take pictures now, and add them to your stash later at your leisure. Or never! I find that the photos are handy for visually skimming the page to see what you have, but they are certainly not necessary.