To use Crosshairs on your charts, right-click into the Chart, select Properties, and then Show Cross-Hairs.
Please note that Crosshairs might make it difficult to drag and drop the Markups, like Trend Lines, on your Chart. If this is the case, simply uncheck this option until your Annotations are placed, then re-enable Crosshairs.
The option, Use Cross-hairs Sync, will sync the Crosshairs on all Symbol Linked Charts.
If you move the Crosshairs on one chart, they will move in sync on all other charts that have this option, as well as Symbol Linking, enabled. This is particularly helpful when monitoring a stock on various time frames.