Ek sit op die stoel en lees die boek.

“Ek” means I. It’s the first-person singular subject pronoun, just like I in English.
Examples:
• Ek sit – I sit / I’m sitting
• Ek lees – I read / I’m reading

In Afrikaans the present-tense verb doesn’t change for person or number. You always use the stem:
• ek sit
• jy sit
• hy/sy sit
• ons sit

Afrikaans has no separate continuous (progressive) tense. The simple present covers both habitual and ongoing actions.
So Ek sit en lees can mean either:
• I sit and read.
• I am sitting and reading.
If you want to stress “I’m in the middle of reading,” you can say: Ek is besig om te lees (I am busy reading).

• die = the (definite article)
• ’n = a / an (indefinite article)
Thus:
• die stoel = the chair
• ’n stoel = a chair

op means on. To say “sit on the chair,” you use sit op + object:
• sit op die stoel = sit on the chair
You could also combine with other prepositions if the furniture changes:
• in die stoel = in the (arm)chair
• op die bank = on the couch

en means and. It links words, phrases or clauses. Here it joins two actions:
• sit en lees = sit and read

Each verb phrase has its own object:
• sit op die stoel – “sit on the chair”
• lees die boek – “read the book”
The conjunction en simply connects the two verb phrases.

• lees is pronounced /leːs/ (long ee, like “layss”)
• boek is pronounced /buːk/ (Afrikaans oe is like the “oo” in “moon,” not the “oo” in “book”)