Translation:I have heard that you have a new girlfriend.
I think in one position it means "brand spanking new", fresh off the assembly line new and in the other position it means "new to me". I assume it means "new to me" here.
This the fourth time in one day that I have seen nueva appear before a noun. I have no idea about rules, exceptions et al, but I plan on putting it in front of any nouns I want to. Es mi nueva idea.
Some example I learned in the French course:
Él tiene un coche nuevo - He has a brand new car. "new" is an attribute.
Él tiene un nuevo coche - It can be a used car, but new to him.
"Nueva novia" is subjective, while "novia nueva" would be an objectively new girlfriend (which doesn't make much sense).
For a clear example, consider "yo compro una casa nueva" (I'm buying a house that was just built) vs. "yo compro una nueva casa" (I'm buying a house that is new for me, regardless of the age of the building)
Generally, the present perfect tense (Yo he oído - I have heard) describes an action that started in the past and continues in the present.
The simple past tense (Yo oí - I heard) describes an action that was completed in the past.
So for your examples:
Yo oí - I heard (I heard it once in the past)
Yo he oído - I have heard (I heard it in the past, and I keep hearing about it)
I'm using a picture of Adelle to remember this sentence. Maybe she'll release a spanish album
If oir is already conjugated to oido then why is tener conjugated as well? I thought that any verbs following another were to stay in their basic form. Is this just an exception?
Oído is a participle, not a conjugation. Haber is conjugated to he before it, and tener is in a relative clause.
I left out the word "that" and was marked wrong :( imo it should still be counted as correct that way tho, in english there's no functional difference between "I have heard..." and "I have heard that..."