Creating a donor letter
welcome to civicrm stackexchange.

You can generate receipts as PDF files to then print and post. You can do this via the Contact's 'contribution' record or via Find Contributions eg at

http://dmaster.demo.civicrm.org/civicrm/contribute/search?reset=1

if you tick a Contribution, then under Actions you can see both


Receipts - Print or Email
Thank you letters - Print or Email.


Pls add comments below, or embellish your question with more details if this doesn't answer your question.

You can read more about this in the Documentation

Also, in terms of StackExchange protocol, if an Answer is helpful, give it a +1, and if it gives you the Answer you need (ie you might get several answers) then 'accept' it.