do dimensions exist or not

Well... we know that in our perceivable world there are at least 4 - height, width, length, and time - but there may be more that we simply cannot detect. Think about it. Length measures in one direction. So does height and width. Here's where it gets more complex. Time is a bit different, but it's basically the same. Time also measures distance from one point in space-time to another. Think of it this way. There is a cube floating through nothingness. This cube is our cosmos. In this cube, you can measure height, width, and length. Outside the cube, you can also measure time. The cube is 3 feet high, by 3 feet wide, by 3 feet tall. Those are tangible measurements. The cube is also located at a certain point in the linear measurement of time. Measuring how old something is puts the object on that line, on a point in the graph of time. Now, what if time could also be measured in three dimensions like matter? What if time could be seen going up and down, instead of just forward and backward? Then we would have more dimensions, branching off from ours. Whenever you make a decision, you go up or down in that graph of time. When anyone makes a decision, you go up or down on that graph. The other way is the other choice, the other path you may have taken, which means that if that theory is correct, if inter-dimensional travel was ever feasible, we could go back in time, and explore an infinite number of realities. We could explore every possible outcome of every possible event that ever occurred!Sorry for making such a long post, I just got so interested.

There are, indeed, many dimensions. It takes a lot of study to learn where they are and how to find them, but many aren't all that hard.

A line drawn on a piece of paper is a 3d object in we zoom in enough.. But a line as an abstract object is monodimensional. Our world has at least 3 spaace dimensions so basically every real object has at least three dimensions given the proper magnification. There are anyhow plenty of objects that can be approximated without much error to 2d or 1d things.

Actually, I think that the line you speak of is actually a two-dimensional object that was portrayed on a three-dimensional object (the paper). This is based only on the definition of dimension that someone came up with... Just look up "dimension" in Wikipedia, as I'm afraid of copying the sentences here, and you'll find some pretty nifty explanations and definitions of what a dimension is... I think that dimension is dependent on your point of view, and looking at that line you can see that it is indeed two dimensional, because you can only see it on the paper.