If we are talking about direct military aid, then the answer is "not very." The German intervention probably shortened the war by a few months, but even without it, the Reds would've lost.

The volunteer, almost totally amateur Red forces were defeated by the conscripted White army, which was trained and led by seasoned veterans from the Jaeger Battalion 27. However, this indirect aid may have been decisive: beginning in 1915, Germany had trained the 27th Jaegers from Finnish volunteers who sneaked to Germany in order to gain military experience for what they believed would be a coming war of independence against Imperial Russia. Instead, they ended up as the leaders of the White army, against revolutionary Reds - a development which did not please in the slightest those Jaegers who had been recruited from the working class, most of whom (about 200) were detained in Germany as a result.

The 700 or so Jaegers who arrived to Vaasa on the 25th February 1918 were very well trained and had combat experience from the Eastern Front: compared to a handful of volunteer Russian advisors, most of whom were not conversant in Finnish, and some briefly participating military units the Reds had on their side, the training and leadership advantage these men provided was simply overwhelming - even though numerically the forces were about equal. The decisive battle for the city of Tampere began on the 16th March; after exceptionally vicious combat between the Whites and greatly improved, much more determined Reds who knew that defeat would mean summary executions (the Whites did indeed execute some 1000 prisoners, about half of the total Red deads during the battle), the battle ended in a surrender of the few remaining pockets of resistance on the April 6th. The German Baltic division had just landed at Hanko on the southern coast on the 3rd, just as the decisive White assault against the Tampere's center began. The Germans met mostly sporadic resistance from the few Red units remaining in the rear, and their only real combat action was the taking of Helsinki from 1500-2000 Red guards between 11th and 13th of April. This operation was strategically insignificant, although it may have saved Helsinki from similar destructive urban battle that had been seen in Tampere. That said, for the Reds the disciplined German troops were the better enemy to surrender to, as they were very unlikely to simply shoot their prisoners and did not have kangaroo courts that handed out death sentences very liberally. However, after the prisoners were handed over to the Whites, many were executed nevertheless.

The commander-in-chief of White forces, General Mannerheim, knew that his forces would defeat the Reds on their own, and as a former Czarist general, he disliked and distrusted the Germans. He did not approve that the White senate had asked for German military intervention, nor did he want the Germans to take Helsinki (he wanted to conquer it himself) but acquiesced nevertheless, resigning only after the war as the German advisors started to organize new Finnish Army on a German model.