in the A1 level we have three main cases (Nominative, Accusative, Dative)

Nominative

in the Nominative case we have few things that point out to the Nominative first => the question tools :
1 - was

Accusative

there are few things change with the Accusative :
1 - der => den
2 - ein => einen

if you want to know how to know the Accusative in the sentence there are few things to point out:
1 - wen
2 - wohin
3 - was

Also the prepositions that comes with Accusative :
1 - bis
2 - durch
3 - gegen
4 - fur
5 - ohne
6 - um

A huge note about how we can know if the sentence accusative, is the verb you don't need to memorize the verbs in accusative, what you need to do is do the opposite by memorizing the Dative and the Nominative verbs.

these are few examples about the Accusative case :

• was ist das ?
• das ist ein buch
• was ist das fur ein buch ?
• das ist ein buch fur kinder
• was ist das fur ein buch fur kinder ?
• das ist ein buch fur kinder zum lesen
• was ist das fur ein buch fur kinder zum lesen ?
• das ist ein buch fur kinder zum lesen in der schule
• was ist das fur ein buch fur kinder zum lesen in der schule ?

Dative

there are few things change with the Dative
1 - der => dem
2 - ein => einem

if you want to know how to know the Dative in the sentence there are few things to point out:
1 - wem
2 - wo
3 - woher

Also the prepositions that comes with Dative : 1 - an
2 - auf
3 - bei
4 - mit
5 - nach
6 - seit
7 - von
8 - zu
9 - am
10 - gegenuber
11 - vor
12 - auser
13 - aus

Also a huge note about how we can know if the sentence is Dative, is the verb in the sentence and there about 50 verb from A1 - B2 that you need to memorize.

these are few examples about the Dative case :

1. Der Arzt gibt dem Patienten eine Spritze. (The doctor gives the patient an injection.)

2. Sie wartet auf den Bus an der Haltestelle. (She waits for the bus at the bus stop.)

3. Ich schenke meiner Mutter einen Blumenstrauß. (I give my mother a bouquet of flowers.)

4. Der Lehrer erklärt den Schülern die Grammatik. (The teacher explains grammar to the students.)

5. Ich danke dir für deine Hilfe. (I thank you for your help.)

6. Sie trägt die Tasche über der Schulter. (She carries the bag over her shoulder.)

7. Die Katze sitzt auf dem Sofa neben dem Hund. (The cat is sitting on the couch next to the dog.)

8. Wir gehen ins Kino mit unseren Freunden. (We go to the movies with our friends.)

9. Er erzählt der Frau von seiner Reise. (He tells the woman about his trip.)

10. Er erzählt der Frau von seiner Reise. (He tells the woman about his trip.)

11. Das Kind hat Angst vor dem Hund. (The child is afraid of the dog.)

Summary

to understand Dative and Accusative you have to know that nominative is the subject and then you need to know that the object depends if you have one object the check out the verb in most cases it's Accusative, learn the verbs that require the Dative case, if you have two objects then usually the person in Dative and the thing is Accusative.

possessive pronouns