Help me understand how this sentence was created.

たなかさん は としょかん に いきます
Tanakasan.......toshokan........ikimasu
mr.Tanaka.......library............to go

I don't understand why this sentence has a は linking a person with a library. What is the function of this は ?

I also don't understand why に is linking a library with going. Can someone explain the use of these two は, に ? That way I can use them to write my own sentences.

Even in English, "Mr Tanaka library to go" is not a sentence, it's just some random words. We need to add some grammar to make a proper sentence.

は and に are particles that are attached to the ends of words to indicate their grammatical role in the phrase.
は is the topic particle, and marks the topic in the sentence (who or what you're talking about). In this case, the topic is Mr. Tanaka.
に in one of its meanings, indicates the direction of a movement, like the English preposition "to" (but it goes after the noun).
としょかん = (the) library
としょかん に = to (the) library

So: たなかさん は としょかん に いきます = Mr Tanaka goes / is going to the library.

I understand now.

gracias.