This is a space that's rather new for me. Given my lack of deeper understanding of the space, I tend to defer to existing vehicles. Generally, I like to take about 40-50% of my paycheck an put it into savings. The remainder is used for rent and living expenses.
Of the money allocated for savings, I distribute my it into two buckets: passive investing account (Wealthfront) and high yield savings account. The distribution is around: 40% Wealthfront and 60% rainy day savings. My approach is more on the conservative side, but you can research and find other approaches to savings and investment depending on your risk.
A general useful philosophy is to have a rainy day cache fund that should support you for at least 6months. For example, if your monthly expenses (rent +util+ food + other living essentials) is $500, you should aim to have a cash savings of at least ($3,000). This money you should never touch, but continuous add to. That saving should be in some sort high yield savings account (~1%). Most high yield savings accounts tend to be online banks (https://www.nerdwallet.com/blog/banking/best-high-yield-online-savings-accounts/) but sometime you may find local banks with competitive rates.
Passive investing is investing your money in a diversified portfolio of low-cost index funds. An index fund usually tracks the market. For example a fund could own a small share of all the companies in the S&P500. A lot of research shows that passive investing strategies tend to outperform most short-term market investment strategies. There is a slew of companies that automate the passive investing for you using bots.
These companies (Wealth Front, Betterment, Wealth Simple) usually have the same strategy. Depending on what your risk profile is, they invest your money in a mixture of bonds and ETFs. If you are looking for aggressive returns, they will weight your portfolio to emerging markets and Asian markets, while conservative risk policies will favor municipal bonds. The strategy for young adults is be more on the aggressive side with passive investing. As I mentioned above, I use Wealth front because they have really low service costs (.25% of your portfolio) and the first 10K is managed for free.
Finally, I try to max out my contributions my roth IRA every year. A Roth IRA is a retirement savings vehicle that allows you to defer taxes on your investments (taxes are levied upon withdrawal). You can contribute up to 5.5k per year.
So I've thrown alot out there. Feel free to ask question if any of this is confusing.