The maximum limit is $5,500, plus an additional catch up contribution of $1,000 if you're over 50 years old.
However, depending on your income and tax filing status, the maximum amount that you can contribute can be less than the maximum limit. Please see this page on the IRS website for more details.
From your question, I think you are a bit confused with the concept of IRA. Think of it as a "basket", where you can hold different investments, which may include money market options, stocks, bonds and others. You can invest in the money market or the stock market with your personal money. And you can do so with your IRA money for the tax benefits that the IRA plan offers.
The question of what to put into your IRA depends on many factors, including your age, income, debt, retirement goals, risk tolerance and so on. It's best to study your options carefully to understand the pros and cons of each option. Usually, it's recommended to add a mixture of investments into your portfolio to offset the risk. You can work with a financial advisor to determine the best allocation for you.