>>4790586
Before you install OpenRCT, first install RCT Classic (or RCT Deluxe on GOG). There's an automated "tutorial" on the main menu.
You can also watch it here around 5:36 (last time I remember, the game actually annotated instructions through a nice step-by-step process)
https://www.youtube.com/watch?v=xw6UlMlJ3oI
Then, as >>4790676 suggested, install RCT2 and OpenRCT (with RCT classic installed, you can integrate its features into OpenRCT too). Start with the fail-proof coasters:
Giga Coaster (able to tolerate high drops and turns at intense *banked* speeds)
Twister Roller Coaster (experiment with inversions of loops, corkscrews, etc.)
Spiral Coaster (of the three I suggest, this is easily the best one for beginners as the limitations of height forces you to gauge momentum of going through hills. Not to mention, this specific coaster has the most lenient stats of all the coasters)
But in the end, indulge yourself with death coasters, learn, and have fun.