1. Descendant selector: It targets elements that are descendants of another element. It uses a space between selectors. For example, div p selects all <p> elements that are descendants of <div> elements.

2. Child selector: It targets direct child elements. It uses the > symbol between selectors. For example, ul > li selects all <li> elements that are direct children of <ul> elements.

3. Adjacent sibling selector: It targets an element that directly follows another element. It uses the + symbol between selectors. For example, h2 + p selects the <p> element that directly follows an <h2> element.

4. General sibling selector: It targets elements that follow another element, regardless of their position. It uses the ~ symbol between selectors. For example, h2 ~ p selects all <p> elements that follow an <h2> element.

5. Grouping selector: It combines multiple selectors into a single rule. Selectors are separated by commas. For example, h1, h2, h3 selects all <h1>, <h2>, and <h3> elements.

6. Attribute selector: It selects elements based on their attributes. For example, [type="text"] selects all elements with the attribute type equal to "text".

These are just a few examples of how selectors can be combined in CSS. By using combinations of selectors, you can precisely target specific elements or groups of elements on a web page.