1. Open Editor
2. Copy this:

sv_cheats 1;
sv_infinite_ammo 1; //or 2
ammo_grenade_limit_total 5;
mp_warmup_end;
mp_freezetime 0;
mp_roundtime 60;
mp_roundtime_defuse 60;
sv_grenade_trajectory 1;
sv_grenade_trajectory_time 12;
sv_showimpacts 1;
mp_limitteams 0;
mp_autoteambalance 0;
mp_maxmoney 60000;
mp_startmoney 60000;
mp_buytime 9999;
mp_buy_anywhere 1;
bot_stop 1;
bot_kick; //optional
cl_grenadepreview 1;
mp_humanteam any;
mp_teammates_are_enemies 1;
mp_respawn_on_death_ct 1;
mp_respawn_on_death_t 1;
mp_radar_showall 1;
mp_restartgame 1;

3. Click on "Save as..."
4. Select "All types" on "Data Type"
5. Type in the name of this file: training.cfg
6. Save this file in your Steam folder:
C:\Steam\steamapps\common\Counter-Strike Global Offensive\csgo\cfg
7. Click on "Offline with Bots" in the "Play" section in CS:GO
8. Select a map and start the game (Competitive mode and without bots recommended)
9. Open your console and type in: exec training
10. Now you have entered the training mode

First of all, all possible commands to get a specific grenade:

give weapon_flashbang;
give weapon_molotov;
give weapon_hegrenade;
give weapon_smokegrenade;
give weapon_decoy;

To bind all of them together (5 max.), go to console and type in:

bind [key] give weapon_a; give weapon_b; give weapon_c; give weapon_d; give weapon_e;

(a,b,c,d,e are variables)

I. There are plenty of bot commands, such as "bot_kick", "bot_add" or "bot_place" etc.
II. You can enter "noclip" in your console to fly over the map
III. You can bind keys in the console, e.g.: bind p "noclip"
IV. Google some nice commands for typing into the console :p
V. If you want to be immortal in train mode, enter this in the console: god (IMPORTANT if you dont want to get killed by your own mistakes :D )
VI. If you run out of money somehow, you can still drop guns, e.g.: give weapon_ak47