Make a list of all your expenses. I use an Excel spreadsheet but you can do it on the back of a napkin if you prefer.
List fixed expenses, like rent, loan payments, insurance, etc.
I include giving to church and charity as fixed expenses, but of course that's up to you.
List regular but not fixed expenses, like food, heat and electricity, gas, etc. Come up with reasonable average or typical values for these. Keep records for at least a few months so you're not just guessing. (Though remember that some will vary with the season: presumably you spend a lot more on heat in the winter than in the summer, etc.)
You should budget to put something into savings and retirement. If you're young and just starting out, it's easy to decide to postpone retirement savings. But the sooner you start, the more the money will add up. Even if you can't put away a lot, try to put away SOMETHING. And if you budget for it, you should just get used to not having this money to play with.
Then total all this up and compare to your income. If the total is more than your income, you have a problem! You need to find a way to cut some expenses. I won't go any further with that thought -- that's another subject.
Hopefully you have some money left over after paying all the regular expenses. That's what you have to play with for entertainment and other non-essentials.
Make a schedule for paying your bills. I get paid twice a month, and so I pay most of my bills when I get a paycheck. I have some bills that I allocate to the first check of the month and some to the second, for others, whatever bills came in since my last check, I pay with the current check. I have it arranged so each check is big enough to pay all the bills that come from that check. If you can't do that, if you'll have a surplus from one check and a shortage from the next, then be sure to put money aside from the surplus check to cover the bills you'll pay at the next pay period.
Always pay your bills before you spend money on entertainment.
Always have a plan to pay your bills. Don't say, "oh, I'll come up with the money somehow".
If you have debt -- student loans, car loans, etc -- have a plan to pay it off. One of the most common traps people fall into is saying, "I really need to get out of debt. And I'm going to start paying off my debt. Next month, because this month I really want to buy this way cool toy." They put off getting out of debt until they have frittered away huge amounts of money on interest. Or worse, they keep accumulating new debt until they can't even pay the interest.