Learn French: Si tu t'inscris, l'abonnement mensuel sera moins cher. - If you register, the monthly subscription will be cheaper.

This sentence is included to show the contrast! Si (if) is the most standard way to state a condition, but it is never followed by the subjunctive. When expressing a likely future condition with si, you use the present tense (tu t'inscris) followed by the future tense (sera). You could rewrite this using the lesson's grammar as: L'abonnement sera moins cher à condition que tu t'inscrives.

Why is there a t' in tu t'inscris?

The verb is s'inscrire, which is a reflexive verb meaning 'to register' or literally 'to sign oneself up'. Because it's reflexive, you need the matching pronoun te, which drops its 'e' and becomes t' before the vowel 'i' in inscris.

Why is it moins cher instead of le moins cher?

Moins cher is a comparative meaning 'less expensive' or 'cheaper'. If you added le to make it le moins cher, it would turn into a superlative meaning 'the cheapest'. Here, we are just comparing two options: the price with registration versus the price without.

Why does the adjective mensuel come after the noun abonnement?