For one export- simply click on the Preset name to select.
The Check mark is only to be used when you want to 'batch' export using multiple Export Presets in the same process. (eg. you might want to export a set of TIFs and a set of JPGs in the one batch process.)
Placing a check mark against a Preset prevents changes to the Preset.
Presets that have a grey check box are Presets that cannot be 'Batch' selected.