2 different email addresses- but similar- have converged into the older email address' inbox

I have had email address for 20 years,I have just added another email address- I could not find how to add it to my list of email addresses I Have on laptop. The email addresses are very similar. Just took out 2 letters and added a 2 to new amai address with google. I have installed it somehow on my smartphone which I use a lot. I just checked for message of the new email address on lap top. The email address does not show as listed. But I found messages in old email address, Guess if I can add new email address to those I already have- perhaps problem will be solved for new emi address. Can you show me how to add new address to my list of existing ones? Thanks