I am using R for a multiple linear regression and I would like to test the validity and reliability of my research. Please how do i go about this in R.
Look into the "psych" package, it has many great functions for conducting reliability (e.g., the alpha and omega functions) and validity (at least factor analysis) analyses. You need data on individual items (e.g., answers on single items) in order to conduct reliability analysis, or at least two measurement points of the same construct (retest-reliability).