"Seems" refers to "give the impression." It has the same meaning in both cases. Just a quick correction regarding the first sentence : 'It seems to be..' instead of 'It's seems to be.'
We can use "seems" with an adjective when something gives us the impression of being a certain way. For example: You seem nice. This building seems old. He seems poor. It is also a nice way of saying something we believe is true. For example, "You seem sad, is everything okay?" Instead of directly saying "You are sad."
We can use "seem/s" along with the verb "to be" in the infinitive form. The examples given, can be replaced with "seem/s to be." For instance, "You seem to be nice", "This building seems to be old."
However when we use an adjective + a noun, it is better to use "seem/s to be." For instance, "It seems to be a promising journey", "They seem to be angry people."
I hope this helps! I know the grammar can be frustrating and this is why I think the best way to learn English is to increase your exposure. The grammar would come naturally!