"The dog loves you."
Translation:Köpek sizi sever.
Patience, arkadaşım :) Some things are best learned by examples first, grammar rules later. Otherwise you can't learn the basic grammar.
To answer your question: For general descriptions of an action that lasts over a longer time period, the "geniş zaman" (present tense) is more appropriate. "Köpek seni seviyor" is more like an observation when you are meeting someone with a dog and the dog really seems to like you in this moment. Nevertheless, you could say "seviyor" and it would not be wrong and people would understand you. But the way the present vs. present continous is used, the translation with "sever" is more accurate.
The present tense is formed a bit "irregular" - there are multiple rules for words of different length / syllables in the stem, and a few "special"(*) words. I found a link explaining the three different rules applied to endings for the present tense:
Basically the three cases are:
1) word stem ends in vowel -> large vowel harmony (ı, i, u, ü)
2) one-syllable word stem that ends in consonant -> small vowel harmony (e, a)
3) multi-syllable word stem that ends in consonant -> large vowel harmony
- Regarding special words: I am not entirely sure right now but I do believe there are a few (less than 10) exceptions to the case 2) where one-syllable-words ending in a consonant take a letter in the ending that is not e/a. You'll eventually run into them - or not, if I remember incorrectly ;)