Not sure if this will help due to English being your second language, but here goes:
DECA: Nandrolone is by far one of the most popular anabolic steroids available. This is due to the compound's affinity for being highly anabolic but relatively mild in terms of androgenic side effects. Nandrolone is the base steroid 19Nor-testosterone, meaning that it is like testosterone in appearance except for the absence of a carbon atom in the 19th position. This small change makes a major difference in the characteristics of the compound (1). Notably, this change makes nandrolone a less potent agonist of the androgen receptor. This of course reduces the chance that a user will experience androgenic side effects. Instead of forming dihydrotestosterone when encountering the 5 alpha reductase enzyme like testosterone does, nandrolone will form dihydronandrolone. Dihydronandrolone is extremely mild in terms of it's antagonizing the androgen receptor. Therefore androgenic side effects should be far less likely to occur with nandrolone than with testosterone.
Testosterone: Testosterone is responsible for the development and maintenance of male secondary sex characteristics. This includes it being a highly anabolic and androgenic hormone, therefore being capable of increasing users' muscle mass and strength/power when administered at larger than normal doses in the body. The testosterone enanthate compound itself is an injectable oil which contains testosterone with the enanthate ester attached to the testosterone molecule. When the enanthate ester is adding to testosterone base, it creates a long-acting form of testosterone. This requires a user to only inject the compound once or twice per week to maintain fairly stable levels of the compound, something that is obviously an advantage. Blood levels of testosterone enanthate will fall rather dramatically five days after it is administered, however the level of the compound should still be well above baseline after a week. This is quite similar to the cypionate ester. In fact, testosterone cypionate and enanthate are basically interchangeable in terms of active life and half life, including almost identical release patterns. Enanthate was primarily manufactured in other areas of the world outside of North America. Cypionate was the ester of choice for North American companies in the early stages of anabolic steroid development. However now both of these esters are used throughout the world having both maintained their popularity with users. They are both widely available.
Testosterone is able to promote strength increases and muscular growth via numerous mechanisms. Of course first off testosterone promotes nitrogen retention in muscle therefore allowing the muscles to hold more protein and enabling repair and growth of those muscles. Secondly testosterone binds to the androgen receptor to promote receptor dependant mechanisms for muscular growth and fat loss. Testosterone also helps to increase the concentrations of androgen receptors in cells that are important for muscle growth and repair in muscle(1).
