pH strips - or pH papers - can be used for rough estimation of solution pH. They are made of paper impregnated with pH indicators or mixtures of indicators. To use a paper you have to immerse it in the solution, wait several seconds and compare color of the paper with scale usually printed on the side of the box. Modern pH strips contain several small pieces of indicator impregnated fabric, which makes measurements more precise when compared to older ones - where whole paper was impregnated with identical indicators mixture.
There are different types of pH papers. Most often used are universal strips, that can be used to check pH from the 1-14 range. Less often, but still quite popular are strips prepared for checking pH in much more narrow range, like 3-6, 7-10 or even only two pH units.
Finally there are litmus strips sold in two versions - blue ones, and red ones. Such litmus strips can be used to check presence of acid or base - blue will change color to red if immersed in acid and won't change color if immersed in base. Red work just the opposite.