Silver is useful, like S.H.I.E.L.D. Points, for purchasing items from the store.
How to get Silver:
Silver is earned from completing tasks. A good strategy is to set all of your Heroes to complete tasks before you go away from the game. Then, when you return, you should have an influx of money to greet you. You will also get a bunch of XP from following this guide. So send your best Avengers on 3 minute remote missions while you are actively logged into the game, but when you are leaving the game overnight or for a while, set them to do the longest missions possible. When you return, you will have heaps of coins.
There are 9 possible rewards from completing missions and only 3 of those contain Silver.
You also earn Silver from completing every mission with 2 stars, which will reward you with 1,000 Silver.
Another good strategy is to ask your friends to crew your Jets and upgrade everything to get extra Silver.
Gold has a variety of uses in Avengers Alliance, and is essential for progressing through the game. One of its key uses is to purchase Resources to help you in your battles.
How to get more Gold:
You can earn Gold primarily by levelling up. You can then choose what to spend it on, such as Command Points or S.H.I.E.L.D. Points as described below.
There are no hacks reported for Avengers Alliance yet. If you do come across any, bear in mind that they can lead to your account being suspended or banned, and your game not functioning properly. It also defeats the point of having levels in a game if you are just going to cheat to get through them!
Also, if you get every star on a mission, you have an additional chance of earning a gold reward. Getting four stars on any mission will always reward you with one Gold.
Early on in the game, during the tutorial stages, you should ignore the screens that pop up asking you to spend your Gold on various items. You do not have to do this and you will probably be much better off if you save the Gold and spend it on things that you really need.
Gold and Silver Values:
If you want to purchase Gold or Silver in Marvel Avengers Alliance, below are the amounts that you will have to pay for varying volumes of cash:
4 Gold - $1
20 Gold - $5
42 Gold - $10
85 Gold - $20
240 Gold - $50
500 Gold - $100
800 Silver - $1
4,000 Silver - $5
8,400 Silver - $10
17,000 Silver - $20
48,000 Silver - $50
100,000 Silver - $100