This verse is part of a larger description in Numbers 7 detailing the offerings made by each of the twelve tribal leaders of Israel during the dedication of the Tabernacle. Let's break down the meaning:

"One young bull, one ram, one male lamb a year old...": This lists the specific animals that were to be offered. The variety suggests a rich and complete offering. The animals had to be without blemish (perfect).

"...for a burnt offering;": This indicates the type of offering. A burnt offering was a sacrifice where the entire animal (except for the hide which was sometimes kept by the priest) was burned on the altar as a pleasing aroma to the Lord. Burnt offerings were offered for several reasons:

Atonement: To cover unintentional sins.
Dedication: To dedicate oneself or something to God.
Thanksgiving: To express gratitude to God.
Atonement for moral impurity

In the context of Numbers 7, the meaning is as follows:

Each tribal leader brought these specific animals as a burnt offering as part of the dedication ceremony for the Tabernacle. This was an act of:

Dedication: Symbolizing the tribe's commitment and dedication to God and the Tabernacle.
Atonement: Seeking atonement for any unconscious sins that might hinder their service.
Worship: An act of worship and thanksgiving to God for His provision and guidance.
A symbolic "gift" for the Lord to dwell in the newly dedicated Tabernacle

Symbolic Significance:

Some scholars also point to the symbolic significance of the animals themselves:

Bull: Often associated with strength and service.
Ram: Representing leadership and provision.
Lamb: Symbolizing innocence and purity, often associated with atonement.

In summary, the verse describes a specific part of the elaborate offerings made during the dedication of the Tabernacle. It demonstrates the tribes' dedication, seeks atonement, and expresses their worship and gratitude to God through a carefully prescribed burnt offering.