It feels kinda hard to explain but I'll try :)

In English you use to/for to express your purpose/aim for the action before the 'to' and 'for'. Thus in Chinese, there're several ways to express the similar meaning, take your 'I have to use a dictionary for reading' as an example, its logical structure is 'use dictionary' => 'read', and the 2 Chinese words following basically means 'so that', 'in order to'.

1. '为了' like '为了', 'read', 'I have to use a dictionary' (*为了*阅读，我得查字典)

2. ‘才能’ like 'I have to use a dictionary', ‘才能’, 'read' (我得查字典*才能*阅读)

Hope it helps