Having issues with previewing my html code with Bootstrap template in Chrome Browser

Whenever I try to make changes to my code, it’s not correlating those changes in the chrome browser. I’ve been following a Udemy course to make my first website using a starter template called Jumbotron on Bootstrap. The problem is is that a lot of the links that worked when the guy made the course on Udemy don’t work now in 2019. Anyone dealt with this issue? Here’s my code just in case. i’m also trying to connect my css to my html but that’s for another post. here’s the html i’ve got at the moment- anyone see any issues with this? it’s driving me crazy!

hmm i am not even sure how to show my code on here (i’m a newbie) - if anyone wants to see a particular part of the code i can post it tho)