Mis sandalias están en la entrada; hoy no quiero usar tenis.

Spanish normally uses estar (not ser) to talk about the location of things and people.

• Estar = current state or location
  
  • Mis sandalias están en la entrada. = My sandals are (located) in the entrance.
• Ser = identity, permanent characteristics, origin, definitions, time, etc.
  
  • Mis sandalias son azules. = My sandals are blue.

So you say están en la entrada because you’re saying where they are, not what they are like.

The verb must agree in number with the subject.

• Subject: Mis sandalias → sandalias is plural (like “sandals” in English).
• Therefore you need the plural form of estar: están.

Compare:

• Mi sandalia está en la entrada. = My sandal is at the entrance. (singular)
• Mis sandalias están en la entrada. = My sandals are at the entrance. (plural)

In Spanish, every noun has a grammatical gender, usually masculine or feminine. Many, but not all, nouns that end in -a are feminine.

• la sandalia (feminine, singular)
• las sandalias (feminine, plural)

Some patterns:

• Words ending in -a are often feminine (la casa, la mesa, la sandalia).
• There are exceptions (el día, el mapa), so you learn gender together with each noun.

Because sandalia is feminine, you use:

• la sandalia / las sandalias
• mi sandalia / mis sandalias

En expresses being in/on/at a place (location).
A usually expresses movement towards a place (direction).

• Mis sandalias están en la entrada.
  → My sandals are *at/in the entrance.* (location)
• Voy a la entrada.
  → I’m going *to the entrance.* (movement/direction)

So for where something is, you use en, not a.

La entrada literally means “the entrance”, but in a home context it often refers to the entryway / hallway / foyer—the area by the front door where people might leave shoes, coats, etc.

So Mis sandalias están en la entrada is very naturally understood as:

• My sandals are in the entryway / by the door.

Both are possible, but possessive adjectives (mi, tu, su, nuestro, etc.) before the noun are far more common for simple possession.

• Mis sandalias = my sandals (normal, neutral)
• Las sandalias mías = my sandals (more emphatic or contrastive, like “those sandals of mine”)

Use:

• Mis sandalias in almost all everyday contexts.
• Las sandalias mías only when you really want to emphasize mine vs someone else’s, or in more literary / expressive style.

In Spanish, the subject pronoun (yo, tú, él, etc.) is often omitted because the verb ending already shows who the subject is.

• quiero → must be yo (I)
• So (Yo) hoy no quiero usar tenis. is normally just Hoy no quiero usar tenis.

You only add yo when you want to emphasize or contrast:

• Yo hoy no quiero usar tenis, pero tú sí.
  I don’t want to wear sneakers today, but you do.

Yes, usar can mean “to use” and also “to wear”, especially in many Latin American countries.

All of these are common:

• usar tenis – to wear sneakers (literally “to use sneakers”)
• llevar tenis – to wear sneakers, to have sneakers on
• ponerme tenis – to put sneakers on (focus on the act of putting them on)

Differences in nuance:

• usar: wearing/using as a habit or choice
  
  • Hoy no quiero usar tenis. = Today I don’t want to wear sneakers.
• llevar: emphasizes having them on you
  
  • Hoy no quiero llevar tenis. = I don’t want to have sneakers on today.
• ponerse: the moment of putting them on
  
  • Hoy no me quiero poner tenis. = I don’t want to put sneakers on today.

In many parts of Latin America, usar for clothing and shoes is very normal and natural.

In Latin American Spanish, tenis (as a noun for clothing) usually means “sneakers / tennis shoes”.

So:

• usar tenis → to wear sneakers
• comprar unos tenis → to buy some sneakers

Context tells you whether it’s the sport or the shoes:

• Jugar al tenis = to play tennis (the sport)
• Ponerme mis tenis = to put on my sneakers (the shoes)

In Spanish, you can often omit the article when talking about clothing or shoes in a general, non-specific way, especially after verbs like usar, llevar, tener, comprar.

• Hoy no quiero usar tenis.
  = Today I don’t want to wear sneakers (in general).
• Hoy no quiero usar los tenis.
  = Today I don’t want to wear the sneakers (specific ones we both know about).

So both are grammatically correct; the difference is:

• usar tenis → sneakers in general, no specific pair.
• usar los tenis → a particular pair of sneakers already known in the conversation.

Yes, Spanish word order is fairly flexible here. All of these are natural:

• Hoy no quiero usar tenis. (very common)
• No quiero usar tenis hoy.
• Hoy no quiero usar tenis, la verdad. (with a comment added)
• No, hoy quiero usar sandalias, no tenis. (in a contrast)

Rules to keep in mind:

• no normally goes directly before the conjugated verb:
  • no quiero, no uso, no llevo
• hoy (like most adverbs of time) can go:
  • at the beginning: Hoy no quiero usar tenis.
  • at the end: No quiero usar tenis hoy.

Both orders mean the same thing.

Yes, you can use a semicolon in Spanish much like in English: to separate two closely related independent clauses.

However, in everyday writing, many native speakers would just use a comma or even start a new sentence:

• Mis sandalias están en la entrada, hoy no quiero usar tenis.
• Mis sandalias están en la entrada. Hoy no quiero usar tenis.

The version with the semicolon is correct and clear, just slightly more formal/punctilious.