Yes, IRS letters are difficult to understand.
It's helpful to know the type of notice that you received. If you check the upper right hand corner, there's usually a notice or letter type, as well as the year the letter is about. For example CP2000 is very common and it means that the IRS thinks you left income off your return.
Since you have received a letter from the IRS, you can use the Audit Support Center to get further guidance. Follow this link for more.
If you want to get more information through this forum, respond back with the notice type and more details about the letter.