English sentences are built around a core called an independent clause; independent clauses can stand alone as complete sentences: they have a subject and a predicate (verb). Phrases are groups of words that cannot stand alone because they lack a subject or predicate, but they can be added to a core independent clause. Following is a visual to show the relationship between clauses and some types of phrases and how to punctuate them properly.
First, you need to distinguish between an independent clause and a phrase.


Types of Phrases

1. Infinitive (to + verb) phrases are recognizable because they start with the word to followed by a verb (that is, a word that expresses an action or state, as in go, imagine, or some form of be).
   Ex. 1 to find my house
   Ex. 2 to be a country singer
2. Participial phrases begin with an -ing or -ed form of a verb (action or state-of-being word).
   Ex. 1 being a country singer
   Ex. 2 dressed like a country singer
3. Prepositional phrases begin with a preposition such as in, on, or around. Prepositions go with nouns (person, place, or thing) or pronouns (I, you, he, she, etc.) to show how the noun relates to other parts of the sentence. 
   Ex. 1 at my house
   Ex. 2 to a country singer
4. Absolutes begin with a noun (person, place, or thing) or pronoun (I, you, he, she, they, etc.) followed by an -ing or -ed verb (action or state-of-being word). When the absolute phrase comes at the end of the sentence, it always needs a comma before it.
   Ex. 1 fingers strumming
   Ex 2. She sang her heart out, fingers strumming her guitar.
5. Appositives describe a noun (person, place, or thing) or pronoun (I, you, he, she, they, etc.) and usually come after a noun or pronoun. They are always enclosed in commas when they come in the middle of a clause. comma before it.
   Ex. 1 The country singer, my cousin, 
   Ex 2. That one, my country-singing cousin,  

You can add these phrases to an independent clause in different ways to add information to a sentence. You punctuate depending on where these phrases are added. Complex sentences may contain many phrases and even more than one clause.




Ex. 1. Infinitive phrase. To be a country singer, you have to know sorrow.
Ex. 2. Participial phrase. Dressed like a country singer, she visited my house.
Ex. 3. Prepositional phrase.  At my house, I met a country singer.
Ex. 4. Absolute phrase. Fingers strumming and feet tapping, she sang her heart out.
 


Ex. 1. Infinitive phrase. You have to know sorrow to be a country singer.
Ex. 2. Participial phrase. She visited my house dressed like a country singer.
Ex. 3. Prepositional phrase. I met the country singer at my house.



Ex. 4. Absolute phrase. She sang her heart out, fingers strumming and feet tapping.
Ex. 5. Appositive phrase. I loved listening to that woman, my country singing cousin.



Ex. 1. Infinitive Phrase.  She was, to be perfectly honest, a terrible singer.
Ex. 2 Participial Phrase.  She visited, dressed like a country singer, my house.
Ex. 3. Prepositional Phrase. I met a woman, at my house, dressed as a country singer.
Ex. 4. Absolute Phrase.  She sang her heart out, fingers strumming and feet tapping, like never before.
Ex. 5. Appositive Phrase. I met the woman, my cousin, posing as a country singer.

  When you interrupt the independent clause with a phrase, you may sometimes omit the commas around the phrase if the sentence is easy to understand without them. If you do use commas, be sure to place them around the whole phrase. Absolutes and appositives always need commas when they interrupt an independent clause



Prepositional phrases often do not need commas when they interrupt an independent clause.
Ex. 1. Prepositional Phrase. I met a woman at my house dressed as a country singer.
In the sentence below, however, commas are needed.
Ex. 2. Absolute Phrase with Two Commas.  She sang her heart out, fingers strumming and feet tapping, like never before.
NOT She sang her heart out fingers strumming and feet tapping like never before.