It's always great to try a new QuickBooks platform, Aditya_CPA! You can do a lot of things in the desktop version.
The trial version is only good for 30 days, and you can get the same features as the paid version.
Unlike QBO, the Pro 2019 version is in a one-time-payment plan. However, the support for its online services like E-file and E-pay, direct deposit, online banking, etc. is only good for three years. Thus, if you’ll use it now, its online services will be supported until May 2022. Usually, users will buy a new version after the third year.
By the way, we have QuickBooks Desktop for Accountants, you might want to use it for your bookkeeping service instead. You can check the features and pricing here.
For immediate help, we included in-product articles that you can easily search in QuickBooks. Just press F1 to launch it, and search the topic you like. And as always, you can reach out to us in the Community.