Silver is a common currency, used in a large variety of transactions. You will almost never have enough of it. Fortunately, there are also many ways to gain Silver.
Silver cannot be collected in infinitum; there is a maximum amount that can be kept and anything gained in excess of this amount will be lost. When the Commander's base is first established, there is a 6,000 Silver limit. This limit can be raised by upgrading the S.H.I.E.L.D. Vault, which is highly recommended as many purchases are far in excess of this and other player's viewing your base will not see how much Silver you have, but rather how much you have in proportion to your total. making a higher limit disguise your Silver reserves as a lower amount.
You'll need a lot of Silver to reach the dizzying heights of Marvel Avengers Alliance Tactics, so it's a good idea to learn how to get as much of it as you can.
1) Chores. Whenever a player completes (or re-completes) a task in the game, they are given a reward. About half the rewards grant Silver. Defeating a mini-boss, boss, or epic boss also rewards the player with a S.H.I.E.L.D. bonus random spin, which has a chance at rewarding thousands of Silver at once.
2) Flights. Sending jets out from the Flight Deck will yield Silver upon their return. The amount of Silver will vary depending on the pilot's level, the jet's level, and the flight's duration. While a longer flight will yield more Silver than a shorter flight, the shorter flight will always grant more Silver per hour (if it can be reliably sent out on-time as many times as required).
3) Raids. Whenever the player attacks another player's base, there is a chance at getting a percentage of the defending player's Silver reserves, depending on which section of the base was attacked. This is a mildly controversial method of obtaining Silver, as some other players will not be happy about losing their currencies for any reason and may decide to retaliate and escalate the level of aggression between the two bases. However, it can be assumed that a player of level 1 or 2 with only half or less of their base built can be considered an inactive player. Raiding them will grant less Silver (as they haven't developed their Silver incomes to the same degree as an active player), but is much safer from retaliation. All the same, you have now been officially warned about the risks of PvP.
4) Paying For It. By clicking the Silver Coins icon at the top of the world or base map screens, a player can spend real-world currencies or redeem gift cards to gain up to 1.9 million Silver at a time.
Silver is a popular currency, equivalent to any real-world currency in terms of purchasing power.
1) Upgrading Heroes and Agents. When a hero or agent reaches their current maximum amount of experience points, they can go to the Training Center and train to the next level, provided the Commander has enough Silver to pay for it. Once levelled, all their known skills can be upgraded to the next level as well. About half of these skills require Silver to upgrade.
2) Upgrading Buildings. While not every part of the base requires Silver to purchase and upgrade, it's only the Barracks and Iso-8 Refinery. Everything else demands an ever-increasing amount of Silver to upgrade.
3) Flight Capabilities. The first jet and Quinjet are provided for free. Every new jet and Quinjet can only be purchased with Silver, as will upgrading a jet (although the upgrade will grant you ever better Silver returns per flight).
When another player attacks your base and successfully overcomes your defenses, a percentage of your Silver may be lost, depending on which building was attacked. For this reason, a good base defense is recommended (such as putting heroes in the buildings when not in use) as well as spending as much Silver at the end of a play session as possible.