Te-form of copula (-です) and na-adjective (Refer to DBJG Te pp.464 – 467 for more sample sentences.)

This form let adjectives connect to other adjectives or verbs.  

"です" changes into "で" + another sentence. Na-adjective root + "で" + another sentence. Note: You can say “just simply take out “–す.”  A comma can be used right after “de."

In the past, we used these choppy sentences: 名前は、一郎です。　年は１８才です。 せんこうはアメリカ文学(ぶんがく)です。If we use te-form of desu, these sentences can be connected smoothly as follows:

名前は、一郎で、年は１８才で、 せんこうはアメリカ文学（ぶんがく）です。
(lit. My name is Ichiro, age is 18 years old, and major is American Literature.)

The same structure and rule applies to na-adjectives as follows.

このレストランは、きれいで（しずかで）やすいです。
(lit. This restaurant is pretty, (quiet,) and inexpensive.


 

Compare the above sentence with what you have learned.
このレストランは、きれいです。（しずかです。）やすいです。
このレストランは、きれいな、（しずかな、）やすいレストランです。
Lit. This restaurant is tasty, (quiet,) and inexpensive restaurant.

Note 1:  Te-forms do not indicate any past or non-past form.  You need to see the endings of the sentences to see if it is past or non-past.
１０年前、このレストランは、きれいな、（しずかな、）やすいレストランでした。Lit. This restaurant was tasty, (quiet,) and inexpensive restaurant.

Note 2: Do not overuse this structure.  Connecting 2 or 3 sentences is enough; otherwise, it sounds redundant/ unnatural.