Magic Set Editor is the best card creation program out there. Download it and start making cards!

Magic Set Editor is only available for PC, though you can reportedly use Wine. Otherwise, there’s Artifice, a Mac-specific program in early alpha that will hopefully progress. Poke around the Artifice subreddit to find the latest release.

If you can’t use it then MTG.Design is a burgeoning rendering site that is improving in leaps and bounds. If all else, and I do mean all else fails, MTG Cardsmith also exists, but has a pretty poor reputation.