Don't be afraid to ask the question if you're asking it with sincerity (and I truly believe you are).
Yes, it is only the Gospels that are to be placed on the altar.
he signs the book with the thumb of his right hand at the beginning of the Gospel which he is to read, then himself on the forehead, the mouth and the breast: and while the ministers respond, Glory be to thee, O Lord, he censes the book thric From the General Instruction of the Roman Missal (GIRM):
GIRM 122: On reaching the altar, the priest and ministers make a profound bow . . . It is a praiseworthy practice that the Book of the Gospels [having been carried up by the lector or reader -GCC] be placed upon the altar.
GIRM 173: [in reference to a Mass with a deacon -GCC] When he reaches the altar, if he is carrying the Book of the Gospels, he omits the sign of reverence and goes up to the altar. It is particularly appropriate that he should place the Book of the Gospels on the altar, after which, together with the priest, he venerates the altar with a kiss.
And from the rubrics of the Extraordinary Form of the Roman Rite ("Tridentine Mass"):
"These being ended, if it be a solemn Mass, the deacon places the book of the Gospels on the middle of the Altar, and the celebrant blesses incense as above: . . . "
In the Low Mass in the EF, the Gospel is read from the Missal (there not being a separate Lectionary) and is not incensed.
"From the General Instruction of the Roman Missal (GIRM):"
I have some random pasting weirdness going on... silly gremlins in my mousepad.