How do I access/spend the diamonds in my piggy bank from the Primary missions?

Since the developers are trying constantly to charge as much as possible for as little return as possible be careful. The piggy bank maxes out at 250 diamonds and in order to access that you have to (in the US) spend $2.99 to open that piggy bank. Just that 250 diamonds. Every successive time you earn 250 diamonds you will have to spend $2.99 to access it. So if you want the top end sniper rifle, the Ksw87 which costs 3840 diamonds it will cost you $45.93 = (3840 diamonds /250 max diamonds in the piggy bank = 15.36 full piggy banks. Then take that number and multiply it by $2.99 which gives you $45.93). Now of course it’s your choice because the developers of this game, as many others point out on the App Store reviews, are “money hungry” and it’s a business but I think with perseverance you can earn what you need because as soon as you buy one gun there will be another update and your gun that cost you real money will not be as good as a newer gun! Personally I think the game developers are deceptive. I have bought diamonds in the past to buy a better gun and I am currently spending around $12 a month for premium access which is probably not worth it but I’ll kick back some money to the developers because I like the game. Just be careful and know what you are getting into because this could become quite expensive for you if you aren’t careful.

Where do I get the rules and spending aka import to play the game

Buy the piggy bank in ‘packages’. Don’t know what the limit is for the 2nd bank or what happens when the timer gets to zero.

Got 2000 it in there so far. PS; they award you 25 diamonds at a time.

My piggy bank is full. Where do you go to spend the diamonds

If you have full your piggy bank, than you can buy it in 'packages'. It costs 3,49€