In English.....  Aphasia makes it difficult to read, write, speak, or understand speech.  It impairs language comprehension and expression.  It often doesn't affect "thinking" and "intelligence", only language.  It's as though the sufferer is suddenly in a foreign-speaking country.  For example:

"My mother doesn't recognize the word "apple" when we say it, nor can she read the word.  She also can't write or say "apple.  However, she knows exactly what an apple is and could bake a pie with it".  It's the word that she had difficulty with, not the apple.

"Stranger in a strange land"

Receptive Aphasia affects the "reception" of language.  This can make the sufferer feel as though everyone is speaking a foreign language, and everything they read is gibberish. In fact, recovery is more difficult because the aphasic person often must relearn the meanings of symbols  before they can begin to relearn language.  And, because their cognitive (thinking) skills are more advanced than their language skills, they are often frustrated by having a lot to communicate and no way to communicate it.

 "It's on the tip of my tongue"

Expressive Aphasia causes difficulty with producing language.  If you've ever had a name on the "tip of your tongue", then you have  experienced a very mild version of this.  You know exactly what you want to say.  You can describe it, you can draw it, but you just can't think of the word for it.  For someone with expressive aphasia, many or all words are "on the tip of their tongue".  

Read an excellent article on global aphasia

Detailed definition

Aphasia is a language disorder that results from damage to portions of the brain that are responsible for language. For most people, these are parts of the left side (hemisphere) of the brain. Aphasia usually occurs suddenly, frequently the result of a stroke or head injury, but it may also develop slowly as in the case of a brain tumor. The disorder impairs both the expression and understanding of language as well as reading and writing. Aphasia may co-occur with speech disorders such as dysarthria or apraxia of speech which also result from brain damage.

Further reading