In French, to give opinions or state facts about things, it is can be expressed in two ways: either c'est or il est/elle est.
It can be tricky to know when to use one or the other, so here's the way to do it!
1. c'est in sentences it/he/she is + a/the/my... + [thing/people]
If it/he/she is is followed by un/une/le/la... (any form of article / determinant) - it is a beautiful dress / she is a nice person - then you will use c'est.
2. Cases expressing opinions or simple statements (adjectives) about prementioned things, look at these rules:
a - c'est for general, unspecific statements and opinions
In those cases, we're expressing opinions or statements that refer to the thing generally: we're saying science in general is thrilling, or that something unspecified is great or delicious.
Therefore, here we use c'est to say it is.
b - il est/elle est for statements and opinions related to specific things
In those cases, the opinions expressed relate to specific items, we know precisely what we're talking about, whether it be my jumper (not jumpers in general), your plate or that specific bed.
Therefore, here we use il est or elle est, depending on the gender of the thing it refers to (remember that things have genders too in French!).
When using il/elle, you have to make adjectives agree accordingly, whereas you always use the masculine with c'est.
(See Standalone adjectives after c'est are always masculine)
Ambiguous cases in French
Look at these two examples talking about soup:
Note that in French, both statements look identical (Tu aimes la soupe ?) when in English they mean two distinct things:
Do you like soup? is a question on soup in general, whereas
Do you like the soup? is asking about a specific soup, i.e. the one they're eating at that moment.
The tricky fact is that in French, you use the definite article le, la, l' for general statements as well as specific the.
See Using le, la, l', les before nouns when generalising (definite articles).
So here you need to know the context to use either c'est (soup in general) or il est/elle est (the specific soup).
See how to use c'est with adjectives : C'est = It is