expression, ichidan verb
pay a tax
Standard expression for paying taxes; 納める implies fulfilling an obligation.
今年も忘れずに税を納めなければならない。
I must remember to pay my taxes this year too.
More general 'pay taxes'; 税を納める emphasizes the formal act of fulfilling a tax obligation.
Compound of 税 (tax) + を (object marker) + 納める (to pay, to supply). The verb 納める carries a nuance of delivering something due.