well, please tell me how to differently remember STATIONERY and STATIONARY.

Stationary means not moving or in fixed position, while Stationery is a paper with decors and used for letters. I usually pronounce them as how they're spelled. For example, Stationary, the 'A' there in between N and R, I pronounce that as the 'A' in APPLE. On the other hand, I pronounce the 'E' in Stationery as the 'E' in ENVELOPE. That's not the usual case if you have an english/american accent though, but I use it for vocabulary purposes, so I don't confuse myself with those words. I hope that helps ^^