I am still very confused with wrist bp monitor. is the one i have available , arm cuff won't fit. do i put my arm like resting on a table? or do i have to rest my elbow and raise my hand to heart level? readings are very different, i tried both ways?

The usual routine is to place the wrist monitor at the specified location near the wrist fold, and fold the arm placing the monitor close to your heart. It does not matter if you lay down or sit to do this. If you are consistent with technique & have good batteries, you should have relatively similar readings if taken 5 minutes apart. It is reasonable to take a couple readings & record the average