"Please read the letter immediately."
読む is the plain non-past form, that corresponds to the polite form 読みます, built on 読み. 読む is also the basic dictionary, or citation form, for looking the verb up in a dictionary. 読んだ is the plain past form, that corresponds to the polite form 読みました. The verb 'yomu' is a consonant stem (godan) verb, for which the stem is yom-: -u is added for the plain non-past final form (shūshikei), -i for the continuative (ren'yōkei), -a for the negative / 'imperfective' (mizenkei). Joined with a following て or た, the m at end of the stem assimilates (merges), adding voicing, resulting in で だ. Hence, 読んで (the progressive or command form used with ください) and 読んだ (the plain past form). The resulting forms may in many cases be further combined to produce additional forms.
A few examples: From 読み: 読みたい want to read, 読みながら while reading, 読みにくい difficult to read.
From 読ま: 読まないで (negative command form used with ください ...), 読まなければ (if one doesn't read).
There's a neat little graphic in the Wikipedia article on Japanese Verbs (https://en.m.wikipedia.org/wiki/Japanese_verb_conjugation) that you can download too, if I haven't already overwhelmed you with you much info. :-)
I answered with 「すぐに手紙は読んでください」and it was accepted. I'm not 100% clear on the rules for すぐ, but i know how I would interpret the sentences differently. In the provided answer, I see it as saying something like, "As for the letter, read its contents in a single instantaneous instant." Which is not exactly possible outside of manga and comicbooks. Whereas my answer i see as saying, "as for the letter, read it. Start doing this immediately." Does that make sense?
i agree, since word order isn't as rigid in japanese this should be accepted. also, it should be more flexible in terms of its translations. since すぐ translates to both "soon" and "immediately", other translations of both those words should also be accepted:
早速 (which i would argue translates best to "immediately")
i guess the problem is that all these forms are very contextual
I get that は emphasizes the letter as a topic, but does this imply the letter is part of a conversation or situation where the letter was already referenced? As I understand it, one should use が/を to reference the piece of information that is an answer to a question.
Examples: 窓は誰が開けましたか 窓は私が開けました
This is bitterly confusing because I don't know if this can ONLY specifically apply to contrasting entities since there are several topics that do not need to be contrasted (this question included), so I would deeply appreciate some clarification.
を is a pretty neutral statement "please read the letter immediately"
は marks "letters" as the topic of the conversation implying that the letter is something known to both the speaker and the listener and already in the conversation, "As for the letter, please read it immediately". It also adds emphasis and shows contrast "read the letter, not something else"