1.something是不定代词,谓语动词用第三人称单数,所以用there is
2.there is something very important that you must know about中的that you must know about是定语从句,that作为先行词代指前面的something,将先行词带到句子中去是you must know about something,如果about后面再加上it这句话就不成句子.
3.and连接的两个分句时态一致不是说前面是一般现在时后面也必须是一般现在时,而是保持都是现在时.he's 是he is为一般现在时,后面也要用现在时,故用现在完成时态 has suffered.而且也要看句子的意思来填,这句是说“他时刻为经历困难做着准备,而且已经经历了各种各样的痛苦和困难”.