A chart is a picture of price changing over time, broken into equal time slices.
Every price chart shows three things: time on the bottom axis (left to right), price on the right axis (low to high), and a row of vertical bars in between. Each bar is one slice of time. The slice is called a 'timeframe' — five minutes, one hour, one day, whatever you choose. Try clicking the timeframe buttons above the chart. Same data, three different views — that's the whole lesson in one click.
Below is a 5-minute chart of one trading session. Lots of small ups and downs, lots of detail. If you're trying to make decisions every few minutes, you want this much detail. If you're trying to make decisions once a day, this much detail just makes it harder to see the big picture.
On a 5-minute chart, you see every wiggle. Each bar is just 5 minutes of trading, so a one-hour stretch shows up as 12 bars. Day traders use timeframes like this because they care about precise entry and exit timing. The downside: it's easy to react to small noise that doesn't matter at all on bigger timeframes.