DIESER/DIESES/DIESE

[WisalCh]

Please help me with diese dieser and dieses
when and why to use them?

[Windrammer]

Dies, diese, dieser... etc. all mean this, and are declined according to gender/plural and case.

[despina11111]

http://www.germanlanguageguide.com/german/grammar/demonstrative-pronoun.asp

https://www.duolingo.com/comment/1252496$from_email=comment&

https://www.duolingo.com/comment/7257?from_skill=2ee17365655cd40aa44e6e24318855fe

I hope this will help :D I've had diffuculties with that too!