First, about wheel's grit you should know before grinding. 36-grit can sharpen most gardening tools; 60-grit is better for chisels and plane irons. Eighty- or 100-grit wheels are best reserved for delicate jobs, like shaping metal model parts.
Second, place the item you wish to grind against the front wheel at roughly a 25- to 30-degree angle, keep it moving, the combination of rough grit and constant motion will keep the metal from overheating. When you grind a metal such as steel with a bench grinder the metal becomes extremely hot. The heat can damage or deform the edge of the tool. The best way to avoid edge deformation is to hold the tool to the grinder only for a few seconds and then dip it in water, repeat this until the grinding work is complete。
If your primary use of a bench grinder Is to sharpen your tools, consider using a low-speed grinder. The low speed will also protect the tools from heating up.