German personal pronouns change form depending on the case they appear in. The dative pronouns are mir (to me), dir (to you, informal), ihm (to him), ihr (to her), uns (to us), euch (to you, plural), ihnen (to them), and Ihnen (to you, formal). Verbs that take the Dativ, such as helfen (to help), gefallen (to please), and geben (to give), require these forms. For example, Kannst du mir helfen? means Can you help me? Ich gebe ihm das Buch means I give him the book, where ihm is the indirect object in the Dativ and das Buch is the direct object in the Akkusativ. The verb gefallen takes the Dativ because the person who experiences the pleasing is the receiver: Das Kleid gefällt ihr means The dress pleases her, or in natural English, She likes the dress.
The accusative pronouns are mich (me), dich (you, informal), ihn (him), sie (her), es (it), uns (us), euch (you, plural), sie (them), and Sie (you, formal). Many verbs take the Akkusativ, including sehen (to see), lieben (to love), and kennen (to know). For example, Ich sehe dich morgen means I will see you tomorrow, Ich liebe ihn means I love him, and Kennen Sie uns? means Do you know us? Notice that sie and Sie are identical in form but differ in case: sie in lowercase can mean her or them (accusative), while Sie (capitalized) means you in the formal register.
Conjunctions connect clauses and dictate the word order. Coordinating conjunctions, such as und (and), aber (but), oder (or), and denn (because), keep the normal word order with the verb in second position. The conjunction sondern (but rather) is used specifically after a negation, as in Er trinkt nicht Tee, sondern Kaffee (He does not drink tea, but rather coffee). Subordinating conjunctions, on the other hand, send the conjugated verb to the end of the clause. The most common are dass (that), weil (because), wenn (when or if), and ob (whether or if). For example, Ich weiß, dass er kommt means I know that he is coming, and Ich bleibe, weil es regnet means I am staying because it is raining. With wenn, you can say Wenn ich Zeit habe, gehe ich spazieren (If I have time, I go for a walk). The conjunction ob is used for indirect yes-or-no questions, as in Ich weiß nicht, ob er kommt (I do not know if he is coming). It is important to distinguish weil from denn: both mean because, but weil requires verb-final word order, while denn keeps the normal order, so Ich bleibe, weil es regnet and Ich bleibe, denn es regnet are both correct but follow different word order rules.