You did not really indicate which part of Gulliver’s Travels you were referring to, so I am going to assume you are talking about the part where Gulliver is helping the Lilliputians in their war against the Blefuscudians (Lilliput vs. Blefuscu). It is important to understand that Gulliver’s Travels is satire and that Jonathan Swift is making fun of the political interactions between England (referred to in the story as Lilliput) and France (referred to in the story as Blefuscu).
On the question of what they did to him, I am going to assume you mean what they did to Gulliver. Both sides have some impact on Gulliver, actually. The Lilliputians wanted Gulliver to engage in their war against Blefuscu. Since he was so big, he could easily crush them. Gulliver, however, told them this was not his fight and said he would help only if he could see the Lilliputians were going to be attacked. “…I thought it would not become me, who was a foreigner, to interfere with parties; but I was ready, with the hazard of my life, to defend his person and state against all intruders.” Gulliver helps the Lilliputians by harnessing the Blefuscudian ships, and, in a non-violent way, preventing Blefuscu from attacking.
During the time he is helping, sailors on the enemy ships are shooting arrows at him, and despite the size of these arrows compared to the size of Gulliver, they hurt him. This, then, is something that was done to Gulliver. Also, when Gulliver returns with the ships, the emperor of Lilliput, seeing his chance to crush his enemy utterly, asks Gulliver to go back and get all the rest of the enemy’s ships. Gulliver replies that he… ”would never be an instrument of bringing a free and brave people into slavery.” As a result, Gulliver falls out of favor with the emperor, and he eventually has to flee for his life.