Dies, Diese, Dieses, Dieser
Can anyone explain the rule of when to use each of these, as I am now at the end of this lesson and still have no idea when to use each one. Thanks.
It is defined by the gender of the noun. "Dies" and "dieses" is used for neuter nouns (the former is more common, but certain neuter nouns always use "dieses", such as "Haus"), "diese" is used for feminine and plural nouns, and "dieser" is used for masculine nouns. All of this only applies to nominative case though. When you throw accusative, dative and genitive cases in the mix, it complicates things a bit.
However, if you're familiar with article declension it's easy to remember. Just remove the D letter from the beginning of the definite article, and then attach the remainder as a suffix to the word "dies" and you have the correct form of the demonstrative pronoun. An exception to this is the definite article "das", which as a demonstrative pronoun is either "dies" or "dieses". Here's how definite article declension works: https://en.wikipedia.org/wiki/German_articles#/media/File:German_definite_article_declension.png
Dieser is the nominative singular masculine base form to be found in dictionaries. Dieser must be declined so that its gender case and number matches gender, case and number of the associated noun (i.e. most likely the noun that follows). Dieser is the base form you'll find in dictionaries.
|Sg. Maskulinum||Sg. Femininum||Sg. Neutrum||Plural|
It's these sort of words that make German grammar pretty hard at first, but hang in there, you can learn it!
Your question is a good (and essential) one, but a really good answer needs more space than a little comment here.
Try checking out this guide on "declensions" (<-- the difference between those versions of 'dies' that you posted) and when & how to use the correct ones!
I love this article that you linked here, but this is soooo confusing!!! Very specifically, when she gets to her first basic example, "Der Mann gibt der Frau das Kind. (‘The man gives to the woman the child’) Dem Mann gibt die Frau das Kind. (‘The woman gives to the man the child’)" I'm like wtf?!!? My brain can hardly make sense of this. I'm going to keep reading and hopefully make it past this one day.