VUSA is an ETF that tracks the S&P 500 index, which itself consists of the largest traded companies in the US (companies like Apple, Coca Cola, and 498 others).
It costs about £40/share right now. You could reasonable expect it to, on average, over the long term, grow by 7% per year.
If you buy 1 share a month for a year, and then stop investing, you’d have spent around £480, and then a year later, if things happened to go well, those 12 shares would be worth £514.
So you made about £30 for pressing the “buy” button in an app 12 times.
If you then just leave it there for 10 years, having forgotten about it, it might be worth £944. So that’s £460 for 12 clicks.
Is that worth it? I expect so
Warning: the above should be considered a best case scenario & things aren’t guaranteed to work out quite that well in the future