Words with bold are the words I do not understand well. Could someone here therfore help me explaining what these words mean?

Hello soudi,
It is said quite often that you should practice talking in English or you will not learn. However, this has a “very bad” effect if you do not have sufficient input of English.
If you do not have sufficient input, the sentences you form will be wrong. If these sentences formed are wrong, and no one corrects you, you will start to think that what you have said is correct. Because of this, your mind will be filled with wrong English sentences. Everything you say, all the sentences you form will be incorrect.
So, if you want to practice talking in English, you “must” make sure that the people around you will be in a position to correct you as soon as you make the mistake. If you want to practice speaking in English, you have to speak English correctly. If you speak incorrectly you “must know” that you have spoken incorrectly.
Unfortunately, most English learners do not have native English speakers around them who will always correct them when they go wrong. In this case, it is wise to first get enough input of the language before you “utter even the first word.”
Input is basically any correct English that you may hear or read. If you listen to an English radio station, that is input. If you read a book, then that is input. If you hear to fluent English speakers talking then that is input. If a fluent English speaker is talking to you in English then that is input. Reading this article is input!

Desireandlovesufficient input
I would say "sufficient exposure to English." It just means hearing/reading enough English to become accustomed to and confident with the language.
Desireandloveenough input of the language
Here again say "enough exposure to the language"
DesireandloveIn this case, it is wise to first get enough input of the language before you utter even the first word.”
"utter" means "speak". This is bad advise, by the way. You need to speak the language to become comfortable with it even if you are not proficient. I talk to native Spanish speakers routinely (in English) who are at best only moderately proficient in English but every time they talk to me (or any native speaker of English, of course) it's a chance for them to improve their proficiency with the language.
But how can I become comfortable with it if I don't have any friends who speak English fluently?