I'm going to engage the ruler like so, and you'll see immediately there's something very very different about the ruler. Open PSD files that even Photoshop cannot open. Make a selection and it will be captured to the clipboard. Hide the controls, take a screenshot to clipboard OR click the camera icon to generate a full resolution image SCREENSHOT: Ctrl+Shift+Cmd+4 (MAC) Windows+Shift+S (WIN) will give you crosshairs. Once you're done, you simply tap done, and the grid becomes active on your screen. These tools range from drawing ellipses to creating curvilinear perspective with the Fisheye Point tool. Drag grid to pan, use scroll wheel or pinch to zoom. It should snap, however, to certain points, so 90 degrees in both cases, just there, like so. Click on the Filter Menu and then Vanishing Point. If you need to draw an angle, then you can tilt the grid over, really really easily. We need to get the Vanishing Point Filter first. You can also pinch to change the grid interval, there, like so, or you can use the slider at the bottom of the screen to change that as well, and you can determine yourself which is easier for you. To engage a perspective grid, simply tap the gear icon at the top right of the screen, choose add from the grids item, and then choose perspective, and you'll be taken into this screen where you can move this cube around to change the horizon line and, by extension, the vanishing points.

Photoshop Sketch makes it easier to draw in perspective using a perspective grid and the ruler.