Most people tend to go on vacations, or they go on and travel to places for business related activities amongst other things. Now when going on vacations, people tend to take some items with them. This is because you need to have a few of your belongings with you, when you travel.
Now these items are often carried in your luggage or in your suitcase. Once common mistake that most people tend to make is when they confuse the two and use them as if they mean the same thing. This is not correct, since the two are two completely different terms.
Luggage generally tends to all the items that someone carries with them when they are going on vacations. What this means, is that all the articles that are being carried loosely or in some form of packaging are all considered to be luggage. This means that all the crates, the backpacks, the cartons of items and many other things are all considered to be luggage. Basically anything that you carry with you is your luggage.
Generally, everyone who is travelling has some form of luggage on them.
A suitcase on the other hand refers to an object in which people carry their items when going on vacations. Suitcases are the most popular items to carry your items in and generally they make up most of the luggage that someone carries with them when they are going out to travel.
A suitcase is generally shaped like a rectangle and has a handle on it. They tend to have wheels on them as well, to make it easier to push and pull them around when you are travelling.