Hi @KGee and welcome to Rstudio community,
I never use fasta files before but there this package, I think, can help u to use fasta files: seqinR.
The doc about this package:
http://seqinr.r-forge.r-project.org/
specifically for fasta files : http://seqinr.r-forge.r-project.org/src/mainmatter/getseqflat.pdf
If u want to go deeper in R programming, I advice u to read this book:
Hope it help,
Rodrigue