unable to equip

Unfortunately, you're not giving enough details of your problem, but I'm going to make some guesses.

Unable to equip your gear:

Do you have enough of the required stats to equip the item?
Read the section of the forums that give advice on builds for the class that you have, and distribute your stat points accordingly. Bear in mind that different classes/builds are geared towards certain equipment types, and you won't be able to equip everything.

Have you have used the item before?
If you have, then it's likely that you have used it until it's endurance dropped to zero, and you need to go to one of the shop npcs and press repair item then select on the item in your inventory (repair all repairs all equipped items)

Is the item a type of ammunition for a bow/crossbow/slingshot?
Make sure that the ammunition type matches: bow uses arrows, crossbow uses bolts, slingshot uses shot. Also, ammunition has weapon levels that it can be used with; check the level of the bow/crossbow/slingshot, to see if the level is high enough to use the ammunition.

Can't fly anymore:

Have you unequipped your wings?
Equip the wings to be able to fly again.

Have you run out of MP?
The starting wings drain 2 MP/sec and when you run out of MP, you can't fly until you get more MP.