The text in an R Markdown document is written with the Markdown syntax. It will render as. To write R Markdown you will need a text editor a program which lets you read and write plain text files.
Its very easy to make some words italic and other words bold.
R Markdown is a file format for making dynamic documents with R. Accurate vertical centering needs character metric information on individual characters which is only available on some devices. Above the Markdown source there is a toolbar to assist editing. You will also need R and the package rmarkdown and all the packages it depends on.