If coming from Montrose-Ouray-Red Mountain Pass, drive on down US 550 to Silverton and do not go into the town. Rather continue right at the junction just west of town and head uphill on US 550 as it switchbacks and climbs to Molas Pass. At the 10,899 ft. pass, (where there's a large visitor pullout area with vault toilets), drive south and west on US 550 for .9 mile to the signed turnoff for Andrews Lake. The one-lane, paved road to the lake is just over .6 mile to the lower parking area, which is intended for day-use only. There is another fork to this road that heads uphill to a higher, and very large parking area that's intended for overnight horse-packing groups, backpackers and others staying longer term. There are picnic tables here and vault toilets. If climbing for the day of backpacking to Crater Lake, use this higher lot.
If coming from Durango on US 550, drive to Coalbank Pass, where there are pullouts for day use hikers on either side of the road. Continue driving north on US 550 for an additional 6.4 miles, first dropping in elevation to about 9,800 ft. at a sharp bend in the highway, then gaining steadily back up to the turnoff for Andrews Lake. The turnoff is signed. If you arrive at the summit of Molas Pass, you missed the turnoff. Turn around, drive back down .9 mile and drive on in and follow the directions above for parking.
Primitive and designated camping opportunities abound in the area. There is a Forest Service campground and trailhead at Little Molas Lake (west of the highway and just north of Molas Pass). The City of Silverton maintains a campground at Molas Lake where you can also find pay showers. The upper parking lot at Andrews Lake we have spent several nights in sleeping in the back of our pickup. There is no tent camping there.