These three structures appear in %+ of interview questions.
Arrays: Ordered, indexed, time access, time search, space. Know: two pointers, sliding window.
Strings: Arrays of characters. Know: manipulation, comparison, palindromes.
Hash Tables: Key-value pairs, time and space for lookup. Know: frequency counting, two-sum pattern, checking for duplicates.
Most "easy" and "medium" LeetCode problems use these three structures. Get comfortable with them before moving to trees and graphs.
For deep coverage, see Sections - of the Data Structures roadmap.