Easy peasy
You can find glycerin at any health food store. I usually get a 16 oz bottle, so that is the amount I will use for this. Since it isn't a whole lot of liquid, it would be better to use either good bud or hash (I used dry ice hash) instead of trim to save space.
Grind your material (1 oz buds) nice and fine, then add to a 1 quart mason jar and pour the glycerine over it. Seal with ring and lid and shake to mix well.
The slow way: Leave in a dark cabinet for about 6 weeks, taking out a couple times a day to shake furiously. After 6 weeks, pour through a fine mesh strainer (such as a permanent coffee filter, not paper) and voila! tincture
The faster way: Using a crock pot with a warm setting, add your ground material and glycerine. cover tightly and cook for at least 4 hours, up to 24. Strain as above and store.
**decarb your material first so you will 'feel' it: place ground material in oven safe dish and cover tightly with foil. Place in cold oven and set temp to 220f and timer for 20 mins. let cool then proceed with above directions.