WHAT IS A HABITAT? It's where a certain group of organisms (called a COMMUNITY) live.
WHY DO THEY LIVE THERE? They settled there because the habitat provides them with what they need: specifically, food & water, shelter and a chance to mate.
There are lots of different ways of studying a habitat to find out what lives there - it really depends on the type of habitat you're visiting. Typical habitats to study are hedge, woodland, field edge, rocky seashore, pond - all these will have a particular community of organisms and will have their own methods of study.
Let's explore a few of them.