Linear Search is the most basic way to find something. It's like looking for your keys. You check one place, then the next, then the next...
We start at the beginning (Index 0). Is 15 equal to 42? No. We move on.
We check Index 1. Is 8 equal to 42? Nope. Still haven't found it.
Index 2 has 23. Still not 42. With Linear Search, we have no shortcuts. We MUST check every single box until we get lucky.
Index 3! We found 42. Success! But notice, we had to check 4 items to get here. If 42 was at the end, we would have checked everyone.
This simple method is O(n) or 'Linear Time'. If you have 100 items, you might have to check 100 times. Simple, but slow for big lists!