One more very important concept is your Emergency Fund.
You should already have 2 bank accounts: chequing and savings. You should keep little in the chequing and pay daily expenses. The savings should have more and will earn a bit of interest income. The combined amount depends on your monthly living expenses and any upcoming large expenses (new car, new appliances, etc.). You should have a minimum of 3 months of living expenses in the 2 accounts but maybe you want 6 months if you are conservative. Add to that any known upcoming large expenses. But your target is based on the concept of how many months of cash reserves you need to pay your bills incase you lose your job until you find a new one or if there is a risk of a large surprise expense (your old car falls apart and you need a replacement). This number, whatever it is ($10k, $15k, $20k, etc.) is your Emergency Fund.
To figure out your monthly cash needs write it all down in major categories and use your online bank statements and the transactions to help. This is your monthly budget. Many people have no clue how much and where they spend. But having this written out (in a spreadsheet) is a good practise as then you can figure out where to cut if you have to. Like if you are spending $500-1000 at bars and expensive restaurants then that is an easy opportunity to cut without much paid. Not so easy cutting a car cost if you have to drive to work. This is also important, as from my earlier post, where you need to find at least 10% of your income (15% is Good, 20% is great) going to your investments. If you canโt find that today, then you need to look where to cut expenses to find it tomorrow. Pay Yourself First.
What you will invest is how much cash you have above that Emergency Fund number. So, if you have $40k saved and your Emergency Fund need is $15K then you can invest $25k. Your day-to-day living needs and Emergency Fund comes first. Then you invest the excess/idle cash. If your cash in your Emergency Fund is growing above your target minth needs then invest it. Keep paying yourself first.