While on Codepen making the Portfolio Project, I tried to make a navbar but instead of the buttons being side by side, they stack on top of one another. At first, I thought it was some of my code so I went on W3schools and copy pasted their code and still had the issue, any help regarding this issue?
If you share the Codepen’s link, it’ll be easier for us to help. 
Either way, just to be sure, are you including Bootstrap in your Pen? And, if you are, keep an eye on the version you included. There are big differences between Bootstrap 3 and 4, so certain things might not work from one to the other.
Use bootstrap 3 for now, you might be using bootstrap 4.
Are u using <ul class="nav nav-pills"> to list the Items?
I used grid method from bootstrap by using row/column in order to fix it.