Idk anything about the french tech tree up to the B1. The B1 has a very bad gun but quite good armour. The best you can do is to try to go with your team and use your high rate of fire to harras the enemy. Also, use your thick armour to soak up damage and save your team.
Once you have grinded past the B1 (i recommend using free xp), you will be rewarded with the BDR G1 B. This thing is my favourite tank of tier V. It has great armour and firepower, so its pretty forgiving for beginners.
Try taking the BDR (and also the B1) to the front lines. The BDR is great at sidescraping and will bounce a ton of shots.
After that, the french heavy line looses its amazing armour for at least 2 tiers, but the ARL 44 also has an amazing gun which is a fun reward for grinding tanks like the B1.