Tick chart for FTSE100, showing each change in the ask or bid price. (If the spread is very tight then the lines may overlap, and only the ask line may be visible.)
As well as a plain tick chart, you can use the "Tick speed" mode to add an indicator showing how long it has taken for the last N ticks to happen. The lower the histogram, the faster the market is moving.
The "Timed" mode still shows each change in the ask or bid price, but the X axis of the chart is set to constant units of time. You can use this to view individual ticks while still being able to distinguish between fast and slow periods in the market.
The "Candles" mode draws tick candles. These are candles which form each time that N ticks happen, rather than being time-based.
The FTSE 100 is a share index of the 100 largest companies on the London Stock Exchange. (There are also other FTSE indices such as the FTSE 250 and FTSE All-Share). Although the FTSE is a broad barometer of the strength of the UK economy and of investor confidence, the FTSE/LSE contains many companies whose earnings derive wholly or largely from overseas activity. Therefore, the value of the FTSE is affected by global business conditions rather than just the state of the UK economy, and by the strength of sterling.