Question
How to send mail automatically when opportunity status changed to
closed/won.
If the event is < 30 days, email immediately, if event is > 30 days,
email at the 30 day mark from time of closed.
so for example.. event is 60 days out, send email at 30 days, not
immediately.
Answer
The general idea of the process will look like:
In case you need to read some data from other objects (not Opportunity) then you will need to add Read data elements to get the data you need.
By using conditional flow you can set different conditions. This is described on our academy: https://academy.bpmonline.com/documents/technic-bpms/7-11/conditional-flow#XREF_73788
Before creating the process, I recommend you to examine the articles about Business process designer and examples of processes on our academy: https://academy.bpmonline.com/documents/technic-bpms/7-11/business-process-best-practices
You will be able to find the information about every process element you are going to use.