Not only do I use them, I 'love' them. Click on support and in the box (search for articles) type in what you are looking for. I think they have the most extensive and useful guide about shipping labels. They even have an article about how they make money on their operation.
If you need an urgent answer, use chat. They respond within a few minutes (I just used them today), or email them, they answer promptly.
Their site is quite simple, I don't think that you really need any special manual. They do import your orders from ebay and post back tracking numbers. You can pay with CC and save additional %.
BTW, if you sell internationally, their 1st class package rates are about 25% less than ebay or stamps.com (for lighter packages up to 4 lbs). But you need to ask them to sign you up for their simple export rate (or whatever they call it).
I sell 30% internationally. Since I started to use them in 03-2019, I have recorded the difference between their and stamps.com rates and so far I saved $1,838!!! vs if I used stamps.com. I am attaching their international rate table, so you can how much cheaper they are.
