Once upon a time immortality was only for the famous or the infamous – now it can be for everyone and I don't see why anyone should be shamed by accusations of "vanity publishing" into forgoing the opportunity.
In the past if you wanted your name to live on after everyone who knew you had gone you had to rely on word of mouth. Stories of great ancestors would be told by each generation to the next and through the years they would evolve into myths and legends.
With the invention of the written word the famous were able to take more control of how they were remembered, but only if they were selected by elite publishers or were wealthy enough to pay for expensive private publication. From the writings of Homer to the tales of Beatrix Potter, books cemented the names of only a select few into history. Very occasionally discoveries of handwritten manuscripts like the Country Diary of an Edwardian Lady would be unearthed and would bestow immortality on someone who would otherwise have disappeared.
Fame, however, has been democratised in recent years and now, thanks to technology, anyone can make themselves immortal and ensure they have a permanent place in history by writing a memoir or an autobiography.
It might be that your book will only be read by one or two of your descendants, and perhaps not for a century or more. It might be that it is discovered by a researcher looking into people who lived in your times or your area, or wanting to find out about your profession or the day-to-day routines of someone of your class, gender or background. For some it might mean that your life story is discovered by another writer who turns it into a best selling novel or a block busting film script. What happens to your story in the future is down to serendipity, but if you write it at least it will exist and will have the potential to be discovered and read after you’ve gone.
If you have a computer and a printer you could just write it and print it, putting the manuscript in a drawer for people to discover, just like that Edwardian Country Lady. But if, like the contributors to this site, you have a bit of technical know-how, or know someone who does, you can put it up on a site like Amazon as an e-book or make it available as a print-on-demand paperback, or you could start by simply recording your life story in a blog.
If you have a bit of money to invest you could hire an editor or a ghostwriter to help, and a designer to make the cover eye-catching. With a bit more investment you could produce as few or as many beautifully bound hardback copies as you want, giving them to friends or relatives. If you run a business you could present copies to customers or shareholders, or use them to promote the business. Not everyone will read every word, of course, but most of them will keep the books, particularly if you write a personal message inside. They will put them on a book shelf to be discovered by others in the future.
Committing your story to print is like writing a letter to the future, and will ensure that you reserve your own small place in it.