The process of learning a second (or third, etc.) language can often seem overwhelming or even impossible, when you are first starting out. Here is some information to put it all into perspective:
The Oxford English Dictionary has over 171,000 words. Most average, educated people have an active vocabulary (words that they can use in writing and/or speaking) of about 20,000 words in their native language. They have a passive vocabulary (words that they can understand through context while reading and/or listening) of about 40,000 words. That means that the average English-speaking American is only actively using a small fraction of the total words in the English language (about 12%).
But, it gets even better! You could understand 89% of every day discourse with a vocabulary of only 1,000 words. With a vocabulary of 3,000 words, you could understand 95%. In other words, you only need to know 1.75% of the English dictionary, to understand 95% of what you read.
So what does this all mean for Spanish? First, it is necessary to understand that these are all just ballpark estimates and may vary depending on who you consult. You will probably find slightly different numbers and percentages depending on which source you are getting your information from and which language you are asking about. (This is where we don't need to be so concerned with the exact numbers or percentages. My intent is merely to show you that you don't need to know everything and that becoming proficient in a language is more attainable than you might at first think.) If you absolutely want to see the numbers, though, here they are. 3,000 words in Spanish should be enough to understand 90% of all written and 94% of all spoken Spanish. 2,000 words should get you 85% of written Spanish and 93% of spoken Spanish. Only 1,000 words should get you 77% of all written Spanish and close to 90% of spoken Spanish. (It is important to remember that the word count does not account for all possible conjugations and forms of a word and knowing Spanish grammar would be necessary to make sense of all of the vocabulary.)
Assuming that you are aiming for 3,000 Spanish words, here is a suggested breakdown from alwaysspanish.com:
2,040 nouns (68%)
780 adjectives (25%)
180 verbs (6%)
40 adverbs (1%)
The most important thing to keep in mind is to be active in your learning. Language learning takes effort. If you are not willing to put in the effort, you will probably find learning a language to be a long and frustrating chore. With some effort and focus, on the other hand, it can be an enjoyable and very rewarding undertaking.
Note: I obtained the information about the number of words in the dictionary, active/passive vocabulary and number of words/percentages of words necessary, from the website www.lingholic.com. The specific numbers of words and percentages for Spanish were obtained through the website alwaysspanish.com.