Learn Dutch: Zonder schroevendraaier kun je deze schroef niet vastmaken. - Without a screwdriver you cannot attach this screw.

Because the sentence starts with the prepositional phrase Zonder schroevendraaier. In Dutch, when you start a main clause with anything other than the subject, the verb and subject swap places. This rule is called inversion, making it kun je instead of je kunt.

Why is there no een before schroevendraaier? Doesn't the English translation say "a screwdriver"?

After prepositions like zonder (without) or met (with), Dutch often drops the indefinite article een when referring to a general tool, instrument, or mode of transport. You could say Zonder een schroevendraaier, but leaving it out sounds much more natural.

How would I add zelf to this sentence if I wanted to say "...you cannot attach this screw yourself"?

You can place it after the subject or later in the sentence: Zonder schroevendraaier kun je zelf deze schroef niet vastmaken (or kun je deze schroef zelf niet vastmaken). In this case, zelf acts as an emphatic pronoun, stressing that you personally can't do it without the right tool.

I see both schroef and schroevendraaier in this sentence. Why does the f change to a v?