What's the function of Thanos' gloves in Avengers: Infinity War?

The “gloves” referred to as gauntlets, are a part of his costume. The left gauntlet, often refered to as the Infinity Gauntlet, (more so when it contains the Infinity Stones which it is designed to house), has no other function than to do that. Without the Infinity Stones the Gauntlet(s) have no special abilities in and of themselves apart from being gloves or gauntlets.

The right-handed “Infinity Gauntlet” seen in Odin’s Vault was a replica.

The Infinity Gauntlet was designed to hold six of the Infinity Stones ( referred to as “Infinity Gems” or “Soul Gems” in the comics).

In the Marvel Cinematic Universe the Infinity Stones are six immensely powerful objects tied to different aspects of the universe, created by the Cosmic Entities

(in the comics they were the remaining fragments left behind of the Infinity Being).

Each stone has a specific capability that grants the the one who possesses them mastery over each aspect of the universe for example; Time, Space, Power, Soul, Mind and Reality. When all the stones are gathered and used together in unison they grant the wielder Omnipotence.

In the MCU so far the Infinity stones have been located in the following…

Tesseract (Space Stone)

Aether (Reality Stone)

Orb (Power Stone)

Loki's Scepter -originally / now- Vision’s forehead (Mind Stone)

Eye of Agamotto (Time Stone)

Unrevealed as yet- (Soul Stone)

So, the “gloves” called gauntlets worn by Thanos serve as matching parts of his costume and the left gauntlet has been modified with slots to house the Infinity Stones which are the source of power not the gauntlet(s), which have no other special abilities.