Git is a software tool to keep track of changes in a file. It also enables share and collaborate on projects with others.
HTML is a markup langugage used to define the basic contents of a website you might make. For example, with HTML you can create, paragraphs, headings and insert images and videos. The layout of this site was created in HTML!. Hit Ctrl,(on OSX Command)+Shift+I to see this site's HTML!
CSS is a style sheet language used to define the style of a website and the HTML elements on the site. Some of the things that you can do with HTML is that you can define the color of the site and reposition the layout of elements on the site
Bootstrap is a free and open-source CSS framework. It has CSS-based templates for text, forms, buttons and navigation bars. Its really cool and helps speed up your development process towards designing a website