First you need to create a request and execute it

self.request = [BDMInterstitialRequest new];
    [self.request performWithDelegate:self];

After polling, you need to save the bid request ([BDMRequestStorage.shared saveRequest:request];)

#pragma mark - BDMRequestDelegate

- (void)request:(BDMRequest *)request completeWithInfo:(BDMAuctionInfo *)info {
    // After request complete loading application can lost strong ref on it
    // BidMachineFetcher will capture request by itself
    self.request = nil;
    // Save request for bid
    [BDMRequestStorage.shared saveRequest:request];
    // Here we define which Admob ad should be loaded
    [self makeRequest];

Then you can create an admob object and load it

- (void)makeRequest {
    GADRequest *request = [GADRequest request];
    [GADInterstitialAd loadWithAdUnitID:@UNIT_ID request:request completionHandler:^(GADInterstitialAd * _Nullable interstitialAd, NSError * _Nullable error) {
        if (error) {
            // fail load
        } else {
            self.interstitial = interstitialAd;
            self.interstitial.fullScreenContentDelegate = self;