is the witch any good? tips?

i made a witch as my first char. cause im a nature witchcraft Wicca freak. anyways i feel really weak with this class at least in comparison to other classes. the campaign seems really difficult for me. am i the only one?

Probably the most important thing to focus on while leveling is getting enough life from the skill tree, and resistance on your gear. Path of exile is not the kind of game where you can go 100% damage in the talent tree and faceroll the game. Every build in path of exile wants to get a large amount of life in the skill tree and even more on gear, as well as stacking your elemental resistances up to the cap(75%). These two stats should be your main focus on every piece of gear. The only exception is on your weapon, which as a spell caster should have spell damage, cast speed, etc.

Witch is intellect based and primarily a caster or summoner class(though you can do almost any build with any class). I would recommend that you choose a spell type skill gem that uses intellect as its primary stat, so you don't have to go out of your way to find strength or dexterity on gear. As long as your chosen skill gem is tagged as a spell you will want to pick up spell damage skill nodes. If it is tagged as fire, you want to get fire damage skill nodes, etc. etc.
If you mouse over this ice spear gem you can read at the very top it says "cold, projectile, spell" this means that cold damage nodes, projectile damage nodes, and spell damage nodes all work on it.

Another area to focus on is what your skill gems are good at doing. A skill like ice spear will generally only hit 1 enemy at a time, so if you choose to make a build using it you will also need a skill that does heavy area of effect damage. You can also choose to support your ice spear gem with LMP(Lesser Multiple Projectiles) or GMP(Greater Multiple Projectiles) to shoot out 3 or 5 ice spears every time you cast it, turning it into a better area of effect skill. For most of the quests in the main storyline you want to have a strong AoE skill and also a strong single target skill to kill bosses with.

Path of exile takes an immense amount of time to understand and especially for new players I would recommend looking up guides and using the wiki heavily but ONLY after you choose a skill that you enjoy. Don't listen to anyone who says "X skill gem sucks" because honestly every skill gem in the game can be used for a legitimate build (except shock nova). Find a skill you like, then look up a quick guide on what is important for you to focus on in the skill tree and what support gems are good to link to your chosen skill gem.

There are several skills/builds that are not suited for beginners (either because you need special gear or need to know what you are doing).

Stay away from:
Low life builds, cast on crit builds, wand builds (good attack wands are rare and expensive), discharge, righteous fire.
I also recommend not trying a Chaos Innoculation build with your first char. Go for a life build.

If you choose a certain element as your main spell, craft yourself a +1 wand or sceptre:
magic wand/sceptre + 1 alteration orb + topaz ring (for +1 lightning) or ruby ring(for fire) or sapphire ring (fore cold).
The extra level for your spell helps a lot in the beginning.

Once you have 1 alchemy orb, visit poe.trade and look for someone online who is selling a Goldrim leather cap for 1 alch. Buy it. The boost to your resistances is HUGE.

If you settle for freezing pulse/ice spear or fireball as your main spell you can check my guides (-> my sig). They are written especially for beginners.