לפעמים השיעור קל, ולפעמים הוא קשה מאוד, ואני רוצה ללכת הביתה.

Because Hebrew often uses the pattern לפעמים ... ולפעמים ... to mean sometimes ... and sometimes .... Repeating לפעמים makes the contrast explicit.

So the structure is:

לפעמים השיעור קל = sometimes the lesson is easy
ולפעמים הוא קשה מאוד = and sometimes it is very hard

This is completely natural Hebrew.

ו־ is the Hebrew word for and, but unlike English, it attaches directly to the next word as a prefix.

So:

ולפעמים = and sometimes
ואני = and I

It is usually pronounced ve-, though its pronunciation can change a little in some environments.

ה־ is the definite article, meaning the.

So:

שיעור = lesson / class
השיעור = the lesson / the class

Hebrew attaches the directly to the noun instead of writing it as a separate word.

In present-tense Hebrew, sentences like X is Y usually do not use a separate word for am / is / are.

So:

השיעור קל literally looks like the lesson easy, but it means the lesson is easy.

This is very normal in Hebrew. In past or future, Hebrew does use forms of to be, but in the present tense it usually leaves them out.

Hebrew does not have a separate neuter pronoun like English it. Every noun is either masculine or feminine.

שיעור is a masculine noun, so the pronoun that refers to it is הוא.

Here, הוא does not mean an actual male person. It refers back to השיעור, so in English we translate it as it:

ולפעמים הוא קשה מאוד = and sometimes it is very hard

In the first clause, the subject is stated directly:

השיעור קל = the lesson is easy

In the second clause, instead of repeating השיעור, Hebrew uses הוא to refer back to it:

ולפעמים הוא קשה מאוד = and sometimes it is very hard

This is similar to English, where we often say the lesson is easy, and sometimes it is very hard rather than repeating the lesson again.

You could also say ולפעמים השיעור קשה מאוד, but the version with הוא sounds natural and avoids repetition.

They are in the masculine singular form because שיעור is masculine singular.

So:

שיעור = masculine singular noun
קל = masculine singular adjective
קשה = masculine singular adjective

Hebrew adjectives must agree with the noun they describe or refer to in gender and number.

If the noun were feminine, the adjective form would change. For example, קל would become קלה. With קשה, the spelling often stays the same without vowel marks, but the pronunciation changes in feminine speech.

מאוד means very, and in Hebrew it usually comes after the adjective or adverb it modifies.

So:

קשה מאוד = very hard
literally, something like hard very

This is one of the common word-order differences between Hebrew and English.

Yes in pronunciation, but usually not in ordinary unpointed spelling.

A male speaker says:

אני רוצה
pronounced ani rotze

A female speaker says:

אני רוצה
pronounced ani rotza

So the written form is often the same, but the spoken form shows the speaker's gender.

This is the same basic pattern as English want to go.

רוצה = want / wants
ללכת = to go

So:

אני רוצה ללכת = I want to go

Hebrew often uses a verb followed by an infinitive this way.

The ל־ at the beginning is the normal marker for the infinitive, like English to.

With many verbs, the infinitive starts with ל־, and ללכת is the standard infinitive of the verb הלך, meaning go or walk.

This particular verb is somewhat irregular, so ללכת is best learned as a whole form: to go.

הביתה means home or to the house/home, and it contains an old directional ending ־ה that means to / toward.

So:

הביתה = toward home / homeward

That is why Hebrew says:

ללכת הביתה = to go home

and not normally ללכת להבית.

This kind of directional ־ה appears in a few common place words and is worth recognizing as a special pattern.