This is a very frequent verb that you will be using constantly, so pay attention because it has three different meanings.
1. Parecerse a: it is used to compare two real persons or two real things. You know them and you can say that they are similar. So, it is a real comparison. In this case, you always use “parecerse a”:
Me parezco a mi hermana. I look like my sister.
Te pareces a tu hermana. You look like your sister.
Se parece a su hermana. He/she looks like her/his sister.
Nos parecemos a nuestra hermana. We look like our sister.
Os parecéis a vuestra hermana. You all (or you both) look like your sister.
Se parecen a su hermana. They look like their sister.
2. Parecer: it is used to say that something or somebody looks in a particular way, but you are not comparing two real things or two real persons, you are describing the aspect of the person or the thing:
Juan parece cansado. John looks tired.
Su casa parece un palacio. Her/his house looks like a palace.
Ella parece una persona importante. She looks like an important person.
To distinguish between cases number 1 and 2, compare this:
Case 1. Ella se parece a su hermana. I am saying that the girl looks like her sister. In this case, I take this as a fact.
Case 2. Ella parece su hermana. I am saying that there are two girls and maybe they are sisters, for example, because both are tall, blonde and pale. In this case, it is not a fact, only a probability.
3. Parecer: we also use it to express our opinion, so we can say:
Pienso que es una buena idea. I think it is a good idea.
Creo que es una buena idea. I believe it is a good idea.
En mi opinión, es una buena idea. In my opinion, it is a good idea.
Para mí, es una buena idea. For me, it is a good idea.
Me parece que es una buena idea. It seems to me that it is a good idea.
