I have a 5-column .csv file, which I have converted to a .root file. I’m hoping to create a 1D histogram using the first two columns (the first column being the horizontal axis).
Hi maveir, you can find more macros and examples that you can also play with interactively at this link.
In particular the basic2.C tutorial shows how to read a CSV directly into a TTree using the TTree::ReadFile method (its documentation is in the ROOT reference guide as usual).
If those resources do not help, show us what you have so far and we can take it from there!