Here's the link to the guide that is posted on the wiki: How to play the original AoM on modern PCs (This guide applies only to people who have the original non-gold edition of the game as a disk)

Assuming that you don't have a disk, there are two options: buying a new disk or torrenting a copy of the game. As /u/Black__Adder mentioned above, you can buy the gold edition from Amazon for $10. The gold edition should work on modern computers. The other option is to illegally download a copy of the game from a torrenting website. Because I don't want to break any reddit or subreddit rules, I won't provide a guide on how to do this, but you could do some googling to find a guide on how to torrent a copy of the gold edition or the original.
I strongly recommend the first option; buying a copy of the gold edition from Amazon for $10. Here's a link to the Amazon page

Amazon or maybe some random local store at discounts (got AoE Collector's that way).

Y, you can buy the Gold Edition e.g. off Amazon and other places.