In my first batch I was very worried about not being able to end it by not having certaing equipment at the right time. The thing is by following strictly the instructions my hydrometer reading was very close to the one predicted in the recipe. But after that I thought to myself 'why i did buy this.. i wouldn't be able to take any correction measure if it wasn't right' So, if the hydrometer it's far from the ideal density in the mashing process what could be done? And one thing related to that. If the reading shows that density it's very close to water and so you want to increase the levels of sugar in the content by increasing temperature (or cooking time), could you eventualy 'burn' your mash? Or you will only lose water? IMPORTANT: i thing for the sake of not getting to vague in the question is better to focus on the appropriate measures for the mash process, fermenting density and other stages could be done in another topic
Two things to note about using a hydrometer during the mash/boil: 1/ you should always make sure your hydrometer is calibrated to 1.000 in distilled water at whatever the calibration temperature of your hydrometer is (usually somewhere around 60°F/15°C). (You only need to do this once, it should never vary over time.) 2/ The temperature of the sample does change the reading. At temperatures close to the calibration temperature, you can compute a correction, but once you get very far away – say up to mash temperatures – I'm not sure the simple computations will still be correct. One way to get around this is to force-chill your samples in the fridge/freezer. (Another way is to use a refractometer, which can use a wort sample so small as to cool it almost instantly.)
If the mash (really, kettle) reading is below your target, then you will want to add sugars to raise the gravity. Some people keep extra liquid or dry malt extract on hand just for this purpose. Sugar can be used, but it is not ideal. If your gravity reading is above your target, then you will want to remove sugars by not draining off as much mash liquor, or dilute sugars by adding water to the kettle.
If you're taking your gravity readings before starting your boil, keep in mind that any reasonable boil length (30-60-90 minutes) will concentrate the sugars in the kettle, which will raise the gravity.
You shouldn't apply heat directly to the mash (under most circumstances). Increasing the boil length in the kettle will evaporate water, leaving sugars behind and concentrating them. A long boil will eventually promote some Maillard reaction, leading to a slight darkening in the kettle.
But if your gravity is really "far from ideal density" and "very close to water", then perhaps something is wrong. Even a low-gravity table beer should have a gravity around 1.030, and most ales are going to have an OG around 1.050/1.060.