How to change layer’s CRS in order to buffer and intersect in QGIS?

Question

I'm very new to QGIS (working with version 3.12).

I'm trying to create a buffer of rail lines, but it's coming out much larger than it should be, e.g. when I try to show a 500-ft buffer, it results in a large circle whose radius far exceeds 500 ft.

I changed the CRS of both the QGIS project itself and the line so that they match, but with the same result. I'm also trying to do an intersect overlay with a line and a polygon and while the resulting layer appears on the panel, it does not appear in the project itself. Again, I matched up the CRS's of the two layers but to no avail.

Something is telling me these two issues are linked. Which problem(s) might I be having? I've attached an image for reference; that little black dot in the middle of the circle are the zoomed-out rail lines from which I'm trying to create a buffer. Again I'm very new to this so please explain as simply as possible as there's quite a bit of terminology I'm not familiar with.

Answer 1

An easy way to reproject a layer is to right-click it in the Layers panel and Export-> Save features as.... In the following dialogue you choose the CRS you would like to reproject to and the format and name of the output. The reprojected layer will be added to the Layers panel by default.

An equally easy alternative for reprojection is the Reproject layer algorithm. It can be found in the Processing Toolbox.

If you use Set CRS, you tell QGIS that the coordinates in the layer are in that CRS (that the layer's CRS is wrong) - this is Not what you want (but is a mistake that many have made before you).