'R' can take various forms in Devanagari script. 'R' itself has variants ( सृजन, प्राण, ऋषि) and it clubs into other alphabets as a half-character too (वर्मा, शर्मा).

For the variants of R, type it using it's sequence (type R repeatedly):

For क्रम, type K R R M .

For कृपा, type K R R R P A.

For ऋषि, type R R R R S S S I.

For using R as a half-character,

For शर्मा, type S S for श, now to insert the र् between the श and the मा, type XRMA. Thus, we get शर्मा by typing S S R X M A.

Similarly use R X whenever you need the matra form of R.