I use coinbase with no middleman, and have for about 2 years.
I love it, no complaints, very simple layout.
Step 1: Open an account at coinbase.com
Step 2: Link it to your checking account
Step 3: Fund your coinbase USD account from your linked checking account. This will take a few days to process. But once your USD account is funded, your bitcoin buys will be instant. Your other options are buying btc straight from your linked checking account (takes up to 5 days to process), or set up instant buy with a CC backup method (but there is a fee). I prefer my method.
Stop, take a deep breath, admire all you have done. No rush to move on to step 4, your money is totally safe, not fluctuating value, and can be transferred back to your checking account in 2 days max if you want.
Step 4: When you are ready to deposit, initiate a bitcoin buy from your USD wallet balance. Yes you can buy fractional bitcoins. The site does the conversion for you. Just specify the USD amount you want to buy and it will convert for you. Very simple. The buy should be instant.
Step 5: At the book, initiate the deposit. You will tell them how much you want to deposit (USD), and they will give you their bitcoin wallet address and the exact amount of bitcoin to send. It is only good for like 30 minutes due to fluctuation and changing wallet addresses, etc.
Step 6: Go back to coinbase, click Send, it will ask how many bitcoin and for a wallet address. Put those 2 things in from what the book told you.
The USD balance will be in your book in 15 minutes tops.
Some people may add a middleman wallet like blockchain in between steps 5 and 6, but I'm too lazy. I figure if I get booted I'll just go to circle and then be more careful. I haven't had any troubles yet.
Note that you can flip flop steps 4 and 5. You could initiate at the book first, and find out the exact amount they want you send. Then go to coinbase and buy exactly that amount (by specifying how many btc to buy instead of how many USD you want to spend). It will prevent you from having odd cents in your account after the deposit. The reason I do it as outlined above is when I initiate at the book, I like to already have the btc in my coinbase btc wallet, so I can immediately send it over before it expires. I'm sure there's enough time to squeeze a buy in there though.
We'll talk withdrawals later. Baby steps.
Ideally you would keep your USD funded with some balance, so you can make instant deposits. When you w/d you can immediately sell it and put the proceeds back into your USD wallet instantly, avoiding fluctuation. You can always w/d from your coinbase USD wallet back to your checking, it takes mine 2 biz days to process.