F in cooking means Fahrenheit which is a unit of measurement for temperature.
The letter G stands for gram in cooking which is a unit of measurement for mass or weight.
Grams are a metric unit of measurement which is used to measure solid ingredients in cooking recipes.
Grams are also used on nutrition labels.
The best way to know how many grams you have as an ingredient is to use a digital sale that converts between metric and imperial measurements.
You can also use a measuring cup or a spoon to estimate the amount of grams.
L in cooking recipes means liters and "mL" means milliliters, Kg means kilograms and °C means degrees Celsius.
An example of measuring in grams would be "one cup of unsifted flour is usually around 120 grams", but the weight can vary depending on the type of flour.
Other common cooking abbreviations for measuring include.
Teaspoon = t or tsp.
Tablespoon = T, TB, or tbsp.
Cup = C or c.
Pint = pt.
Quart = qt.
Gallon = gal.
Ounce = oz.
Fluid ounce = fl oz.