Hi Thefourlions and welcome.
We all started with no idea and well done for finding your way to this Wiki. As Dotgigi says, there is loads of info here so spending some time reading about the tasks, the areas you are playing, and particularly the ‘source items’ (which drop other items) will help you lots.
You specifically asked about getting coins and diamonds. The piggy banks are key for getting both of these. Make sure you pick one up every day. The pro-tip to maximise what you get from these is to get your daily Piggy (level 1) and tap it exactly 14 times to get the coins and gems it contains. A 15th tap will empty it and it will disappear, so don’t do that! Keep it in your inventory (definitely good use of that space) and merge it with the next day’s Piggy, after you have tapped one that 14 times, to get a level 2 Piggy. Don’t tap the merged level 2 Piggy at all. Pop it back in your inventory and wait two days until you can merge it to get a level 3 Piggy. The level 3 Piggy will then drop lots and lots of coins and gems, including some top level piles of coins.
Personally I use the coins to buy as much inventory as I can. I currently have 32 slots but they do get more expensive every time and the next one will cost just under 200,000!
A good way to get money quickly is by playing the Ignatius Bolton event as soon as it is available to you. The mechanics are are bit complicated and it is heavy on energy, but if you sell the Chipper at the start, you just use the other two source items (a Till and a Phone) to generate numbers which you can merge and sell. This will get you lots of money and also lots of XP points to move you up through the levels more quickly. It lasts for 3 days but you can play it as many times as you like.
I don’t know any good way to get more energy quickly. You can buy more with gems but every purchase of energy in a day gets more expensive and I prefer to save my gems to buy source items when they are in the shop. Don’t forget to pick up your free daily energy chest.
As for merging items I will only give you one tip now. Don’t merge the cleaning cabinets past Level 5 unless you are really short of space. Read the Wiki page entries for more details but you can actually reduce the number of items you can get from them if you do so. This is less important with the other source items but again, the Wiki pages give the details so you can decide for yourself.
Enjoy the game!
