YQTL forms (called “prefix forms” by KHW or “imperfects” by most other grammars) are distinguished by the fact that the different forms are made by adding prefixes as opposed to QTL forms which use suffixes. See the charts in the back of KHW page 432, this video or this pdf.
YQTLs are translated into English using the future tense. However, they usually have a vav-conversive in which case it is translated into the simple past tense. These forms are often called “preterite”. Gesenius has much more on translating these. See this video as well.