That isn't how High Valyrian works. Unfortunately, there are rules for some things, but not for others. For example "You are" in High Valyrian is "Iksaa" (with the macron on the a, but this doesn't mean it means "And you are" for example. High Valyrian is a tough language, but keep going and maybe write down the different nouns and translations, and it should eventually start to click. I hope that helps. Let me know if you have any other questions.
The i without the line is like the English "ee" sound. The ī with the line, is the same, but held a bit longer. So like... say: i = beat, ī = bead (if you are a native English speaker, say "beat, bead, beat, bead" over and over, and you will find you hold the vowel longer in "bead" than in "beat.")