More than conjugating verbs by their tense, you more often conjugate based on other factors such as formality, negation, or mood. Japanese grammar is largely about being able to recognize and piece different sentence patterns together. The patterns are often rather logical too; you often just have to subtract one part of a verb and add on another to give verbs different nuances. Verb conjugation, once you learn it, comes pretty easily. There are other parts about the grammar, however, which are a bit more challenging, but not too difficult. Most people start by learning formal verbs (those that end with "-masu"), but I recommend learning the plain form (sometimes referred to as "casual form" or "dictionary form") first and the 3 different categories of verbs and how they change different when conjugated. Those patterns are regular and once you learn them, you'll be able to conjugate all verbs. Then you can start learning all the other forms.