Open Interest is the total number of contracts held by positions opened by traders at any given time. The total number of contracts in open positions can be from both traders who short and traders who long.
So every time you open a short or long position, it means the open interest will increase by the number of contracts in your position, every time you close a short or long position, it means the open interest will decrease by the number of contracts in your closed position.
Therefore when open interest spikes, it means there are so many traders who have opened positions at a given time perhaps in anticipation to a strong movement or the market or trend. If the open interest plunges, it means there are so many traders who had open positions have closed them at a given time perhaps in anticipation to the movement or due to weakened market trend and momentum.
You can't determine market movement alone using open interested. You need to combine it with other indicators like volume. Exchange apps like Bybit can send you notifications of open interest during certain market conditions.
You can also get Open Interest(OI) data from tools like coinalyze -
https://coinalyze.net/futures-data/coins/