How do you start in your 20's investing in real estate? You start with the first one. It's the toughest. Let's think of money in terms of buckets.
Your checking account feeds

short term expenses

Long term savings

outside investments

retirement

Consider setting up automatic transfers.

1 month of expenses, then the remainder rainy day fund, build this account up first.
50% monthly needs housing food - your short-term expenses for living and entertainment.
30% rainy day
20% retirement investment bucket.

To invest in real estate, consider saving $125/month. By the time you graduate college, you can afford to buy a home.
People who invest in real estate are 48x's wealthier than those who rent.