Browse regex building blocks by category and try any pattern in the live tester against your own text to see exactly what it matches before using it in code.
\d matches any digit 0-9. Its opposite \D matches any non-digit, and similar shorthands exist for word (\w) and whitespace (\s) characters.
* matches zero or more of the preceding token, while + requires at least one, so a+ needs one or more 'a' characters.
^ asserts the start of the string or line and $ the end, letting you match patterns only at those boundaries.