looking to use Bitcoin for a purchase, what should i do to make sure i dont lose money in the process?

self.Bitcoin1m ago
im mostly looking for a place to buy from that has the lowest fees (while still being trustworthy), and when to buy + when to use. I already have a wallet on my computer and know some basics on how to use it. I know the value of bitcoin changes quickly, so im under the impression the dollar amount in my wallet also changes. looking at the price on google, i can see i shouldve bought some earlier this week, but i didnt know it was gonna go up. how can i keep up with current events and predict (to the best of my ability) when the value will go up/down?