How does anyone know if they're going to an afterlife? How would I know?

Hi curiousgeorge,
Your own experience is the best answer to your questions. You can gain the information you need for visiting the afterlife by reading thru related topics on the afterlife section of this site--there are 84 pp just of index titles.
Or better yet get a copy of ' Afterlife Knowlege Guidebook' by Bruce Moen, host of this site.  His experiences have been organized in this book into a progression of activities that will take you into afterlife contact. No particular religious faith is necessary except a faith in the power of kindness and consideration---love.
Proof of that contact comes from you asking that soul something that only that soul would know, and then verifying the information here. You might want your first contact with someone you know who has passed over so that confirmation of what they tell you is easier.
No one will force you to believe their experiences but those who have had such experiences are sure.
bets