Macbook Pro crazy green and black, horizontal, checkered pattern, glitching back and forth until it shuts itself off?

My macbook pro (late 2013 model) will glitch out like this for a day or two, then go a month with nothing happening, then it'll act up again for a day or two. It's been doing this for about 6-8 months. It would typically happen about 20 seconds after I turned my computer on or as quick as 5 seconds. After it had done it a few times it wouldn't happen again for an hour or two, then act up again. Today marks the day where it happened all day instead of off and on. I just want to know what's wrong with the dang thing and fix it.