starting up

is it better to lease or buy an aircraft and what is depreciation and how does it affect the airline

I buy,and lease, but most people lease. Since your new to the game I’d do leasing, after a week you can cancel the lease and try another aircraft. I’d also recomend B737-700 BGW and Dash 8 Q400a if you lease.

Depreciation is the value your aircraft looses. It is not a cash deduction, just a reduction in your companies value.

I went with the enmbraer 195 and 737-700 bgw for short routes such as LHR to FRA or AMS should I use standard or economy seats

There´s no precise answer for your question. Just try it out. There is no instruction book for this game and it´s different from game world to game world.

… But you should use economy :)