EA QV TeamRe: star wars the old republic: mount locked in collection
I can see a few things from the screenshot you took. The icon for the STAP is greyed out, which means you're not eligible to use it. This can either be because your level is too low, you don't have the Speeder Piloting skill to use it, or the STAP is already in your abilities.
Since the tooltip says Locked in Collections, that would suggest you haven't learned the vehicle yet. Once you learn the vehicle on one character, it will be unlocked for that character in the collections, and you can purchase an account-wide unlock, usually for 1 Cartel Coin for this vehicle.
If you're at least Level 20, visit your trainer and make sure you have the Speeder Piloting skill, then open your Skill Window (hotkey: P) and go to the Vehicles section to see whether you have the Longspur STAP. If you don't have it, transfer the item to your inventory from your Cargo Hold and try to consume it.
