El proceso de selección necesita la descripción del puesto.

Because the subject is El proceso de selección, which is singular. The main noun is proceso, so the verb must agree with that:

• El proceso ... necesita
• Los procesos ... necesitan

Even though selección also appears in the phrase, it is part of de selección and is not the subject.

Literally, proceso de selección is process of selection. In natural English, that becomes selection process, recruitment process, or hiring process, depending on context.

Spanish often uses the pattern:

• noun + de + noun

where English might use:

• a noun before another noun, or
• an adjective

For example:

• proceso de selección = selection process
• centro de salud = health centre
• mesa de madera = wooden table / table made of wood

So de is very common here.

Spanish uses articles more often than English. So El proceso de selección is perfectly normal, even in cases where English might sometimes say:

• The recruitment process
• or just Recruitment

In Spanish, leaving out the article here would usually sound incomplete or unnatural. El proceso de selección sounds like a specific process being discussed.

Nouns ending in -ción are usually feminine, so they take la:

• la descripción
• la selección
• la información
• la decisión

This is a very useful pattern to remember.

Because de + el contracts to del in Spanish.

So:

• de + el puesto → del puesto

This contraction is required in standard Spanish.

A similar contraction happens with:

• a + el → al

For example:

• Voy al trabajo = I’m going to work

One important exception: if El is part of a proper name, you do not contract it:

• de El Escorial (not del Escorial in that case if El is part of the name)

In this context, puesto means post, position, or role — basically the specific job position.

There are related words, but they are not always identical:

• puesto = position/post/role
• trabajo = work/job in a more general sense
• empleo = employment/job, often more formal

In HR language, descripción del puesto is a very common phrase for job description.

Using la descripción del puesto suggests a specific job description — the one for that role.

Using una descripción del puesto would mean a job description, which sounds less specific.

So the difference is similar to English:

• la descripción del puesto = the job description
• una descripción del puesto = a job description

Both are grammatically possible, but they do not mean exactly the same thing.

Because necesitar normally takes a direct object with no preposition:

• Necesito ayuda
• Necesitan más tiempo
• El proceso de selección necesita la descripción del puesto

English also works similarly here: needs the job description.

You do not use a before the object here because it is a thing, not a person. The personal a is generally used with specific people:

• Veo a María
• but Veo la oficina

Yes. Se necesita la descripción del puesto is also very natural, and it sounds a bit more impersonal.

Compare:

• El proceso de selección necesita la descripción del puesto = more explicit; the subject is stated
• Se necesita la descripción del puesto = more impersonal, like The job description is needed

Spanish often uses se to avoid naming who or what is doing the action.

In a workplace or HR context, selección often refers to recruitment or staff selection, not just the general idea of choosing something.

So proceso de selección can often be understood as:

• selection process
• recruitment process
• hiring process

The best English translation depends on context, but the Spanish phrase is very common in HR.

Yes, but the original order is the most neutral and natural.

Standard order:

• El proceso de selección necesita la descripción del puesto.

You could move things around for emphasis, for example:

• La descripción del puesto la necesita el proceso de selección.

That version is grammatical, but it sounds more marked or emphatic. For a learner, the original sentence is the best pattern to use.