As this mountain is nothing but a walk-up it's quite hard to say where the climb really starts. If you start from Plaza de Mulas, the approach is described in the "Getting There" section on the main page. If you start from a point higher up on the slopes of Aconcagua, from for ex. Camp Canada; see below.
Start from Plaza de Mulas, the base camp of Aconcagua. Walk towards the upper parts of the large camping area. Cross the little river, close to where the ice of the glaciers are visible. You can also cross the river further down in the deeper parts of the valley, but the scree sections on the other side are much steeper and harder.
The switch-backing scree paths takes you first over a small shoulder from where you can see some lighter colored rocks higher up. Walk towards these along the path you like best, there are lots of them to choose from. The place at the rocks is a good place for a break if it's a windy day.
Next step on the walk is the stretch to Camp Canada, which is situated at the foot of some other large rocks. If you want to head straight for Manso and give Camp Canada a miss, head to your left in order to avoid the steep last part up to the camp spot.
When you have passed Camp Canada, you can basically head straight for the summit of Manso, even though you will have an easier walk if sticking to the paths, which eventually will take you to Nido de Condores Camp. If you choose to go on the paths as long as possible, continue until you reach a small, flat ridge. You are now about 60-80 vertical meters below Manso and even if the last part is slightly steeper, it's nothing but a last scramble to the yellow summit. The views on the other side is stunning!
Walking poles, warm clothing, some snacks and liquid. I met some local climbers who used normal jogging shoes to get up to the summit of Manso, but more sturdy boots are of course recommended as the weather can change very fast in the area.
The described route is a good day hike and I used it as a test for Aconcagua. When acclimatized and with a small day-pack you can do this hike in about three hours.
If you don't want to have a lot of people around you in Nido de Condores or if it's really windy and you need a good place to camp, there are some very sheltered places on the northern slopes of the peak. Soft sand for the tent, lots of rocks to pin it donw with and very good protection from the wind from big rocks. Semi-permanent small snow fields nearby for snow-melting.