Learn French: D'abord, tu mesures le mur. - First, you measure the wall.

It is made of the word de and the noun abord (which means an approach or onset). Because abord starts with a vowel, de drops its letter e and becomes d'. Together, the phrase means first or first of all.

Can I put d'abord somewhere else in the sentence?

Yes, you can put it at the end! Tu mesures le mur d'abord is also completely correct and very common in everyday French. Putting it at the very beginning, like in this sentence, is just a great way to structure step-by-step instructions.

Why use tu mesures (you measure) instead of giving a direct command?

When explaining a process, French speakers often use the normal present tense with tu or vous to walk someone through the steps (just like saying First you do this in English). You could use the command form (Mesure le mur), but using tu sounds like a friendly, step-by-step guide.

Do I pronounce the s at the end of mesures?

No, the -s at the end of mesures is completely silent. For regular -er verbs, the tu form always adds an -s in writing, but spoken out loud, it sounds exactly the same as the je or il/elle forms.