How do I enter transaction to my investment account?

It's highly, highly, highly unlikely that you'll be able to "back fill" 11 years worth of history with downloads. Your Financial Institution (FI) MIGHT be an exception, so knowing what FI holds that IRA would help others do a little research to see if that's possible. Most FIs limit downloads to something like 90 days worth of transactions, some allow more, but unless your FI does have the ability to give you the entire history of your account you'd almost certainly be facing manually entering what could be - depending on your investing history - many hundreds of transactions manually.

A more practical approach would be to pick a "start date" for the Quicken Account where you establish your holdings - each security listed, information as to number of total shares owned, and the cost basis of those securities. Most brokers would have that information available to you. Then you move forward from there, populating the transactions from your starting point with a combination of manual and downloaded entries.

As a test you could create a new Quicken file with only that account in in, connect the Quicken Account to the broker's account and get the initial download. That would give you a good idea of what you're facing in terms on the number of transactions that may have to be entered manually, (depending on the FI's ability to provide even older transactions through downloads), and select a "getting started" point that you're comfortable with.

Then abandon that file and go over to your "live/real" file and get started in earnest. (The "history" of transactions down loaded into a file is kept within the file itself, so your "live/real" file will accept those initial downloaded transactions again as "new" transactions.)

Unless you're in the "distribution" phase of your IRA, i.e., you're pulling money out of the IRA, there will be little connection between your checking account and the IRA beyond contributions you're making. All dividends, interest, gains and losses on sales, and expenses will occur in the IRA Account itself. If you are in the distribution phase those transactions will continue to be recorded in the IRA and as you pull money money out of the IRA these will be recorded as "Transfers" FROM to IRA TO the checking Account.

Depending on the FI you're using you can download transactions into that Checking Account too.

One not of caution: YOU are the chief accounting officer of your "enterprise" (file) so you do need to have some understanding of what's going on in your Accounts and pay attention that transactions are recorded properly. Take the position that Quicken helps YOU do your accounting, it doesn't DO YOUR accounting FOR YOU, and you'll have success. Quicken can take a lot of tedium and work out of keeping your accounting straight, but you need to keep an eye on what's going on.