This has probably been asked answered before... but Japanese kanji have two fundamental types of readings.
on (音) - which are readings of the character that originally come from China and approximate the sound of the Chinese character at the time. e.g. 極楽(ごくらく,gokuraku)
kun (訓) - which refer to using a Chinese character in part of a non-Chinese origin native word. e.g. 楽しい(楽しい,tanoshii)
Comparing the two above 楽 gets pronounced "raku" in the on reading instance and "tano" in the kun reading.
name (名) readings are readings used in names which is kind of its own ball game of mostly native pronunciation.
To know which one you want, you can look for what is call okurigana (送り仮名). For many kun- readings, there will be 送り仮名 after the character (e.g. 楽しい). Otherwise, you will have to learn/guess based on context. There are some hints but no absolute rules, i.e. pairs of character tend to be on-yomi.