public class ExampleBlock extends Block {

    public ExampleBlock(Settings settings) {
        super(settings);
    }

    // For versions below 1.20.5, the parameters should be "BlockState state, World world, BlockPos pos, PlayerEntity player, Hand hand, BlockHitResult hit"
    @Override
    public ActionResult onUse(BlockState state, World world, BlockPos pos, PlayerEntity player, BlockHitResult hit) {
        if (!world.isClient) {
            player.sendMessage(Text.literal("Hello, world!"), false);
        }

        return ActionResult.SUCCESS;
    }
}