These particles are very similar to だけ, but they're syntactically different.
しか and ほか are quite odd because the sentence that they are used in must be in the negative for the affirmative. The particle しか can be after nouns, quantifiers such as しか and particle phrases such as those with に, で, and まで. It may also be after nouns. ほか is often after こそあど and may also be after verbs.
In translation, these particles are most often translated as "just/only" after nominal phrases and as "there is no choice but to" after verbal phrases. As for ほか, it strongly limits something. So, in some situations it is not applicable.
Particle Note: The particle に may be deleted before しか!
There's only one week left.
The deadline for the seminar report is tomorrow. I have no choice but to work on it all night long.
Is this all there is for snacks today?
What else did he say?
Grammar Note: You may also use だけ and しか together creating だけしか. Also, しか may be seen as しきゃ and っきゃ in slang.
I have no choice but to do it.
I have no choice but to tell （in advance）.
You have no choice but to just walk.
8a. ローマ字だけ書けます。 I can only write Roman letters.
8b. ローマ字しか書けません。 I can't write anything but Roman letters.
Particle Note: Although だけを is possible and relatively common, the equivalent with しか, をしか, is very literary and doesn't show up that often.
Since I could only believe the beauty that I could see in my eyes, this attitude is natural.
From 金閣寺 by 三島由紀夫.
Time slid by.
Set Phrase Note: いつしか ＝ いつの間にか知らないうちに. It doesn't need to be used to be with the negative.
When not with the negative, ほか means "aside from".
Five in attendance aside from the company president.
To search the rest.
The lawyer explained orally aside from the use of documents.