Particles are used together with words to mark their grammatical role in the sentence.

私(は) - I (subject)
ホテル(の)向かい(に) - hotel (possessive) across the street (to)
(お)店(で) - (just makes the sentence more formal) shop (in)
スーツ(を) - suit (object)

Fun thing about particles is that word order is a lot more flexible compared to English. As long as the right particles are attached to the right words, you can sometimes* swap around the order of these words and still be grammatically correct.