The grandfather
The word 'Der Großvater' is a noun in German, used to refer to one's father's father. It is a compound word, with 'Der' being the definite article for masculine nouns, 'Groß' meaning 'grand' or 'great', and 'Vater' meaning 'father'. It is a common word in German and is used in a similar way to the English word 'grandfather'.
The grandfather reads the newspaper
This sentence employs the present tense to describe an ongoing action by the grandfather, who is the subject. The verb 'liest' which means 'reads' agrees with the subject in person and number. 'Die Zeitung' which means 'the newspaper' is the direct object of the action.
Tom's grandfather is very old
This phrase uses the 'von' preposition to indicate possession, in this case, showing the relation between Tom and his grandfather. 'Ist' translates to 'is', and 'sehr alt' means 'very old', describing the state of Tom's grandfather.
The grandfather plays with the kids in the park
This sentence describes an action taking place in a specific location. 'Spielt' is the third person singular form of the verb 'spielen' which means 'to play'. 'Mit den Kindern' is a prepositional phrase indicating who the grandfather is playing with, and 'im Park' indicates the location of the action.