Best way to learn grammar rules?
I do not quite get the basic present tense rules for German. It sounds to me that a lot of conjugations are different and not all endings are the same. Should I just try to memorize the words that don't have common endings or are there more rules I'm unaware of?
In most languages ,including German and Spanish, verbs conjugate in both regular patterns and irregular patterns. This can be a pretty complex area and whole books are dedicated to verb tables detailing how verbs are conjugated. The best advice at this stage is to keep practising with Duolingo and in the first instance study how regular verbs conjugate in the present tense before moving onto the irregular ones. The best way to absorb the rules is to practice. The tips and notes at the bottom of Present1 on the German course gives an outline of the framework regular verbs follow, demonstrating the stem and endings used.
After that with practice you should build up an understanding of how the conjugations work , mainly through making mistakes and correcting them .
Most German verbs follow the same conjugation pattern in the present tense: remove the 'en' from the infinitive [gehen = geh] and then add the correct ending for the appropriate pronoun: -e, -st, -t, -en, -t, -en.
ich gehe, du gehst, er/sie/es geht, wir gehen, ihr geht, sie gehen, Sie gehen
As others have noted, every language has numerous exceptions to a basic rule. In addition, many of the verbs commonly used in any language are often those which are the most irregular.
The following site provides a quick reference for German verb conjugations as you work through the Duolingo program: