Don't give up to soon...  There are a lot of shortcomings to QBO.  Keep asking your questions and the QB staff or the rest of us will get things worked out.

So were you able to find or did you add a Cash Account?  If you don't use the Home window, there is a button in the menu bar.  This may be on the left side of the QB's window (default) or it may be across the top (where a lot of people move it).  In the Home window you should see a Account Balances on the Right....   Is there a Cash Account (could be Cash On Hand or some other "Cash" related name)? 

If not... as mentioned before, you can easily create one (just like you'd have to create it in QBO if it's not in your Chart of Accounts).  Also in the Home window there is a Company section and there should be a Chart of Accounts icon.  Click on that icon (or just hit Ctrl/A) and the Chart of Accounts will open.

• In the lower left corner click on Account, then New
• Click on Bank, then Continue
• Name the Account (e.g. Cash or whatever you want)
• Save & Close

You can then enter a opening balance for however much Cash you have on hand HOWEVER, make sure you have your Tax Accountant review this initial entry at some point to make sure it is correctly entered and does not mess up your books at tax time.

Once that's done, when you can register all of your Cash payments though this account. 

If you do not usually use a Cash Account.  Make sure that money added into cash either track back to Income from a customer/client or you show a transfer from your Bank (e.g. Checking) into this account if you did take the money out of the bank.