L'escursionista segue il segnavia.

Because in Italian, the singular definite article is often shortened before a vowel.

• il / lo
  • vowel → l'
• la
  • vowel → l'

Since escursionista begins with e-, Italian uses l'escursionista.

So the apostrophe shows elision: the article has been shortened before a vowel sound.

It can be either masculine or feminine.

Many Italian nouns ending in -ista work this way:

• il turista / la turista
• il pianista / la pianista
• l'escursionista can mean a male or female hiker

In this sentence, l' does not tell you the gender, because it is used for both masculine and feminine before a vowel. Usually, the gender becomes clear from:

• context
• an adjective
• a past participle

For example:

• L'escursionista è stanco = masculine
• L'escursionista è stanca = feminine

Because the subject is third person singular: l'escursionista = he/she follows.

The infinitive is seguire. In the present tense:

• io seguo = I follow
• tu segui = you follow
• lui/lei segue = he/she follows
• noi seguiamo = we follow
• voi seguite = you all follow
• loro seguono = they follow

So segue is the correct form for the hiker follows.

It is not completely regular.

It belongs to a group of -ire verbs with some irregular present-tense forms, especially in the singular and third person plural:

• seguo
• segui
• segue
• seguiamo
• seguite
• seguono

So a learner should memorize its present tense rather than assume it behaves like a fully regular -ire verb.

Because seguire is a direct transitive verb in Italian.

You follow someone or something directly:

• seguire una persona
• seguire un sentiero
• seguire il segnavia

So you do not say seguire a or seguire al in this meaning.

Because not every Italian noun ending in -a is feminine.

Segnavia is a masculine noun, so it takes il:

• il segnavia

Italian has several masculine nouns ending in -a, for example:

• il problema
• il tema
• il clima

With segnavia, the article tells you clearly that it is masculine.

It is a compound noun, written as one word.

It is formed from elements related to the idea of marking and way/path, which is why it refers to a trail marker or waymark. Compound nouns are very common in Italian, and their gender is something you often need to learn together with the word itself.

So it is best to learn it as a complete unit:

• il segnavia

Because Italian often uses definite articles in ordinary statements where English might sometimes be more flexible.

This sentence presents:

• the hiker
• the trail marker / waymark

That makes the sentence sound like it is talking about a specific hiker and a specific marker, or about a clearly identifiable situation.

If you wanted a more indefinite idea, you would change the articles, for example:

• Un escursionista segue un segnavia
  or, if feminine,
• Un'escursionista segue un segnavia

A helpful approximation is:

• segue → SEH-gweh
• segnavia → seh-nya-VEE-a

Two useful pronunciation points:

• gu + e in segue sounds like gwe
• gn in segnavia sounds like ny, similar to the sound in lasagna

So segnavia is not pronounced with a hard g as in English signal. The gn is a single Italian sound.