How do i enter previous year transactions in new quickbooks?

Great question!

Enter past sales and A/R, as well as past vendor and A/P transactions, before entering any past checking or bank transactions.  QuickBooks Online updates your bank balance as you enter payments received from customers and payments to vendors.

Customer Transactions (A/R) 
There are two ways to enter sales and A/R transactions.  Both methods ensure accurate reporting.

1. Chronologically:  Enter transactions (charges, invoices, credits, payments) in the same order they were created or received.  This method creates a record of all the invoices you sent.
2. In Batches:  Enter all charges and credits that customers already know about, followed by payments received.  Print a single invoice for each customer to clear their invoice record of the past activity.  Then enter remaining charges and credits you haven't informed customers of, and start sending real invoices. This method doesn't leave a record of invoices you sent.

Vendor Transactions (A/P) 
As you enter your A/P transactions, enter the dates of the original transactions. Enter your historical bill transactions in the following order:

1. Bills:  Go to the  Vendor Center then click Create Bill and enter each bill received between your start date and today. Be sure to assign amounts to the correct expense accounts.
2. Credits from vendors:  Got to the + Symbol then Vendor Credit to enter credits received between your start date and today.
3. Payments:  Go back to the Vendor Center then  Make Payment, record each bill payment made between your start date and today. 

4.     

• Be sure the Payment Date field shows the payment date.  

Entering Banking Transactions

• If you're entering historical transactions for more than a one-month time frame, enter the transactions one month at a time and reconcile all bank accounts before going to the next month. 
• If you're using online banking to download some of these transactions, you need to be aware that we can't provide more than 90 days of downloads from online banking.  Anything before the 90 day period will need to be manually entered.  However, you might be able to get information older than 90 days by using Web-Connect.   Please see our KnowledgeBase article KB 2627, How do I use Web-Connect?: https://community.intuit.com/articles/1145233.
• If you've used online banking to download up to 90 days of history into an account, the Opening Balance is the first entry on the bank register and by default it's marked Reconciled.  If you're going to enter historical transactions either by manual entry or by using WebConnect so your bank register entries go back farther than 90 days you'll need to delete the Opening Balance Entry created by QuickBooks Online Banking Admin and enter the opening balance for the date you're starting your historical transactions using the method described above and then move forward with your data entry.

I hope this helps! 

Thanks for visiting the Community, @cyndithompson.

It’s my pleasure to lend a hand with emailing customer statements in QuickBooks Online.

With QBO, you can create and email statements for single or multiple customers. Here's how:

For a single customer:
1.    Go to the Sales menu and select Customers.
2.    Choose the customer you want to create a statement for.
3.    From the Actions drop-down, select Create Statement.
4.    Select the type of statement you want to create.
5.    Set the Statement Date, Start Date, and End Date.
6.    Click Apply.
7.    Hit Save and send.

For multiple customers:
1.    Go to the Plus icon and select Statement.
2.    Select the type of statement you want to create.
3.    Set the Statement Date, Customer Balance Status, Start Date, and End Date.
4.    Click Apply.
5.    Choose the recipients.
6.    Hit Save and send.

Here’s an article that tackles more about this: How to create and manage statements.

That should get you pointed in the right direction. Please let me know if you have any questions about statements, I’ll be more than happy to answer them for you. Thanks for dropping by and take care!

On many banking sites or credit card sites you can download transactions that are older than 3 months and import them into QuickBooks.  

Lots of good answers here. Hope that at least one of these answers solves the problem!