Account Mix refers to the variety of accounts you have open i.e. loans, credit cards, car loans, etc. Having a variety of account types can positivity impact your score by illustrating to lenders that you are a responsible borrower. Do keep in mind that account mix is only a low impact factor.
There are two types of credit:
Revolving Credit - this is when you borrow against a line of credit. There is no specific end date or set balance involved but rather a minimum payment is due each month. Credit cards are the most common type of revolving credit.
Installment Credit - this is when you borrow a set amount of money. A fixed end date is set and you have a series of payments due every month. Examples of installment credit include student loans, mortgages, or auto loans.
If I only have credit cards, is it worth getting a small loan or vice versa?
If this is something you can afford, it can be worth considering if you're wanting to achieve the perfect credit score; however, it's not advisable if it would negatively impact your payment history or credit utilization factors. Having only one type of credit will not a significant impact on your score.